Method of producing higher-purity glass element, high-purity glass element, and production method and device for glass tube

ABSTRACT

An object of the present invention is to provide a method of highly purifying a glass body, which enables high purification of the glass body while decreasing deformation of the glass body at a high degree, to provide a highly purified glass body, and to provide a method and an apparatus for manufacturing a glass tube, which can obtain a highly purified glass tube.  
     A method of highly purifying a glass body according to the present invention is to apply a voltage between electrodes  1  and  2 , which make contact with the glass pipe  11 , in a nearly radial direction of the glass pipe  11  while heating the glass pipe  11  to a temperature within a range less than 1300° C. Further, a method of manufacturing a glass tube according to the invention is to generate a voltage gradient in a radial direction of a glass tube  106  by applying voltages to the inner circumferential side and the outer circumferential side of the glass tube  106  when a glass rod  103  is gradually formed into the glass tube  106  by heating the glass rod  103  to soften the glass rod  103  and by bringing a boring jig  130  into contact with a softened portion of the glass rod  103.

TECHNICAL FIELD

The present invention relates to a method of highly purifying a glassbody, a highly purified glass body obtained by this method, and amanufacturing method and apparatus for manufacturing a glass tube byperforming high-degree purification on the glass tube.

BACKGROUND ART

In recent years, with advancement in optical communication technology,the use of optical fibers has grown. The main methods of manufacturingoptical fibers are VAD method (Vapor phase Axial Deposition method), OVDmethod (Outside Vapor phase Deposition method), and MCVD method(Modified Chemical Vapor phase Deposition method). Especially, anincrease in the bit rate and in the wavelength multiplicity thereof hasresulted in a growing densification of information transmission capacitythereof, and thus reduction in the polarization dispersion of opticalfibers is strongly desired.

In the manufacture of optical fibers, usually, a method of obtainingdesired optical fibers by performing high-speed drawing on formableobjects referred to as preforms is employed. The shape of the opticalfiber takes the shape and quality of the preform. Thus, when a preformis formed, extremely high precision control of the shape and quality ofthe preform is required.

For example, the MCVD method is to deposit glass particles (soot) on theinner wall of a pipe for inner deposition, which is constituted by aglass tube. This glass tube becomes a part of the preform withoutchange. Thus, this glass is required to have small noncircularity andeccentricity ratio, uniform thickness and excellent properties. Anoptical fiber manufactured from a glass tube, whose noncircularity oruneven-thickness is large, has a large value of Polarization ModeDispersion (PMD).

Hitherto, there has been proposed a hot carbon drill press-in processfor forming a silica glass pipe by pressing a boring member, such as acarbon drill, against a glass ingot which is heated while rotating theboring member (JP-A-7-109135).

Also, there has been proposed a method of heating and softening an endof a columnar silica glass rod while rotating the rod, and of engaging atip end of a boring member with a central part of an end surface of therod, and rotating the glass rod surrounding the tip end of the boringmember with respect to the boring member while drawing the rodcircumferential edge part (Japanese Patent No. 2,798,465).

These methods are referred to as piercing methods. The piercing methodis to form a glass body 201 into a glass tube 205 gradually from afront-side part of the glass body by making a boring jig 202 abutagainst the glass body 201 and pressing the boring jig 202 against theglass body 201 while heating the periphery of the abutted part of theboring jig 202 by a furnace 203, as illustrated in, for example, FIG.25. At least a part of the boring jig 202, which makes contact with theglass body 201, is formed of a material, for example, carbon, which isavailable at the softening temperature of glass and difficult to reactwith glass.

However, it is frequent that impurities are included into the glasstube, which is obtained in this manner, in the step of manufacturing aglass ingot or in the step of boring by a boring member. In recentyears, with increasing demand for improvement in the performance ofoptical fibers, glass tubes having higher purities in comparison withconventional glass tubes have been needed.

In Japanese Patent No. 2,726,729, it is described that a technique ofdiffusing metallic impurity ions from an outer wall surface of a fusedsilica glass tube by applying a voltage to the tube while the tube isheated at a temperature of 1000° C. or higher (in the examples,temperatures of 1500° C., 1600° C., and 2100° C.), and thus, high-degreepurification of the fused silica glass tube can be achieved.

However, the fused silica glass tube obtained in this way shows largedeformation due to the application of heat to the tube. In the case ofapplying this technique to a glass pipe requiring a high degree ofaccuracy of shape, generally, it is necessary to add a postformingprocess, in which the tube is reprocessed into a desired shape,subsequent to the high-degree purification of the glass pipe. Usually,in the postforming process, in order to set the inside diameter and theoutside diameter of the tube to be constant in the longitudinaldirection of the tube, it is necessary to measure the inner diameter andouter diameter over the whole length of the tube and to perform formingon the inner circumferential surface and the outer circumferentialsurface of the tube according to the measured diameters. This may becomea factor in extremely increasing the manufacturing cost of the tube.Moreover, under some deformed condition of the tube, it is verydifficult to manufacture the tube of a desired shape.

Further, a glass rod, in which a glass-pipe hole is not formed yet, isrequired to have a high degree of accuracy of shape and high purityquality. However, it is very difficult to remove impurities, which areincluded into a glass rod when manufactured, while simultaneouslydecreasing deformation due to the fact that the glass rod is heated tohigh temperature.

DISCLOSURE OF INVENTION

An object of the invention is to provide a method of highly purifying aglass body, which enables high purification of the glass body whiledecreasing deformation of the glass body at a high degree, to provide ahighly purified glass body, and to provide a method and an apparatus formanufacturing a glass tube, which can obtain a highly purified glasstube.

A method of highly purifying a glass body according to the invention,which can achieve the object, is to apply voltages, in a nearly radialdirection of the glass body, to at least a part in a longitudinaldirection of a columnar or cylindrical glass body from at least one pairof electrodes placed on an exterior of an outer circumferential surfaceof the glass body.

Incidentally, specifically, a columnar glass rod and a cylindrical glasspipe or the like, which are finished to predetermined dimensions by anappropriate manufacturing method, are used and cited as the glass body.

Further, preferably, the electrodes are plural anodes and pluralcathodes arranged in a circumferential direction of the glass body, anda potential of each of the anodes and a potential of each of thecathodes are respectively set.

Furthermore, preferably, a relative swinging motion between the glassbody and each of the electrodes occurs in a circumferential direction ofthe glass body.

Further, preferably, the method of highly purifying a glass bodycomprises a surface removing process of removing a portion of the glassbody extending from the outer circumferential surface inward to apredetermined depth after the voltages are applied to the glass body.

Moreover, in a method of highly purifying a glass body according to theinvention, which can achieve the object, while a cylindrical glass bodyis rotated around a central axis thereof used as a rotation axis at arotational speed, which is equal to or more than 1 rpm and equal to orless than 100 rpm, voltages are applied, in a nearly radial direction ofthe glass body, to at least a part in a longitudinal direction of theglass body from electrodes disposed at an outer circumferential surfaceside and an inner circumferential surface side of the glass body.Further, preferably, the rotational speed is equal to or more than 1 rpmand equal to or less than 20 rpm.

Furthermore, preferably, a voltage gradient of the voltage is set to bea negative gradient in a direction from the inner circumferential sideof the glass body to the outer circumferential side thereof. Moreover,the method of highly purifying a glass body comprises a surface removingprocess of removing a portion of the glass body extending from an outercircumferential surface inward to a predetermined depth after thevoltages are applied to the glass body.

Alternatively, preferably, a voltage gradient of the voltage is set tobe a negative gradient in a direction from the outer circumferentialside of the glass body to the inner circumferential side thereof.Moreover, the method of highly purifying a glass body comprises asurface removing process of removing a portion of the glass bodyextending from an inner circumferential surface outward to apredetermined depth after the voltages are applied to the glass body.

Further, preferably, the voltages are simultaneously applied to theentirety in a longitudinal direction of an effective portion of saidglass body.

Alternatively, preferably, the voltages are serially applied to theglass body in a longitudinal direction of the glass body.

Furthermore, preferably, when the voltages are serially applied to theglass body in a longitudinal direction of the glass body, portions, towhich the voltages have been applied, are sequentially cooled.

Further, in a case where the voltages are applied in a radial directionof the glass body, preferably, the length in the longitudinal directionof the effective portion of the glass body is equal to or more than 500mm.

Moreover, in a method of highly purifying a glass body according to theinvention, which can achieve the object, voltages are applied in alongitudinal direction of a columnar or cylindrical glass body fromelectrodes placed on exteriors of a first end surface and a second endsurface in the longitudinal direction of the glass body.

Furthermore, preferably, the method of highly purifying a glass body,which comprises an end portion removing process of removing a portion ofthe glass body extending from the second end surface to the first endsurface to a predetermined depth, wherein a voltage gradient of thevoltage is set to be a negative gradient in a direction from the firstend surface to the second end surface of the glass body.

Further, in a case where the voltages are applied in the longitudinaldirection of the glass body, preferably, the length in the longitudinaldirection of an effective portion of the glass body is less than 500 mm.

Moreover, the voltages may be applied without bringing the electrodes incontact with the glass body.

Furthermore, at least a part of the electrodes may be brought intocontact with the glass body.

Further, preferably, the voltages are applied while heating a portion ofthe columnar glass body, to which the voltages are applied, to atemperature that is less than 1450° C.

Alternatively, preferably, the voltages are applied while heating aportion of the glass body, to which the voltages are applied, to atemperature that is less than 1300° C.

Further, preferably, the voltages are applied while heating a portion ofthe glass body, to which the voltages are applied, to a temperature thatis equal to or higher than 450° C.

Alternatively, preferably, the voltages are applied while heating aportion of the glass body, to which the voltages are applied, to atemperature that is equal to or higher than 600° C.

Alternatively, preferably, the voltages are applied while heating aportion of the glass body, to which the voltages are applied, to atemperature that is equal to or higher than 900° C.

Furthermore, preferably, the content concentration of impurity cationscontained in an effective portion of the glass body obtained by thisinvention is equal to or less than 0.01 ppm by weight.

Further, in a high purity glass body according to the invention, whichcan achieve the object, and which is highly purified according to themethod of highly purifying a glass body by applying voltages in a nearlyradial direction of the glass body, the outside diameter of the glassbody is equal to or more than 100 mm, and that the length of aneffective portion is equal to or more than 500 mm.

In the case of the highly purified glass body to which the voltages areapplied in the nearly radial direction of the glass body, when thelength in the longitudinal direction of the effective portion of theglass body is long, the high purification of the glass body is notinhibited by the length. Therefore, the high purification is favorablyperformed on the glass body.

Furthermore, in a high purity glass body according to the invention,which can achieve the object, and which is highly purified according tothe method of highly purifying a glass body by applying voltages in alongitudinal direction of the glass body, the outside diameter of theglass body is equal to or more than 100 mm, and wherein the length of aneffective portion is equal to or less than 500 mm.

In the case of the highly purified glass body to which the voltages areapplied in the longitudinal direction of the glass body, when the lengthin the longitudinal direction of the effective portion of the glass bodyis short, the high purification is favorably performed on the glass bodydue to the short length thereof.

Further, preferably, the content concentration of impurity cationscontained in an effective portion of the highly purified glass body isequal to or less than 0.01 ppm by weight.

Furthermore, in a method of manufacturing a glass tube according to theinvention, which can achieve the object and which has the steps ofheating a columnar or cylindrical glass body to thereby soften the glassbody, and then bringing a boring jig in contact with the softenedportion of the glass body to thereby gradually form the glass body intoa glass tube, when the boring jig is brought into contact with the glassbody, voltages are applied to the glass tube from at least one pair ofelectrodes provided on the exterior of an outer circumferential surfaceof the glass body to thereby generate a voltage gradient in a nearlyradial direction of the glass body.

Incidentally, the “boring” referred to herein includes not only anoperation of making a hole in a columnar glass body but also anoperation of increasing the inside diameter of a cylindrical glass body(or performing diameter expansion).

Further, in a method of manufacturing a glass tube according to theinvention, which can achieve the object and which has the steps ofheating a columnar or cylindrical glass body to thereby soften the glassbody, and then bringing a boring jig in contact with the softenedportion of the glass body to thereby gradually form the glass body intoa glass tube, when the boring jig is brought in to contact with theglass body, voltages are applied between the boring jig and an outercircumferential side of the glass body or to an inner circumferentialside and an outer circumferential side of the glass tube to therebygenerate a voltage gradient in a nearly radial direction of the glassbody or the glass tube.

Furthermore, in a method of manufacturing a glass tube having the stepsof heating a columnar or cylindrical glass body to thereby soften theglass body, and then bringing a boring jig in contact with the softenedportion of the glass body to thereby gradually form said glass body intoa glass tube, when the boring jig is brought into contact with the glassbody, voltages are applied to the glass body from electrodes provided onexteriors of a first end surface and a second end surface in alongitudinal direction of the glass body to thereby generate a voltagegradient in a longitudinal direction of the glass tube.

Further, preferably, at least an edge or peripheral portion of saidglass tube at which the voltage gradient is set to be low is removedafter the glass tube is formed.

Furthermore, an apparatus for manufacturing a glass tube, which canachieve the object and which has a heating element disposed around acolumnar or a cylindrical glass member, and also has a boring jig to bebrought in contact with the glass body heated by said heating element,and which forms the glass body gradually into a glass tube by contactingthe boring jig to the glass body, further comprises at least one pair ofelectrodes provided on the exterior of an outer circumferential surfaceof the glass body.

Further, in an apparatus for manufacturing a glass tube, which canachieve the object and which has a heating element disposed around acolumnar or a cylindrical glass member, and also has a boring jig to bebrought in contact with the glass body heated by said heating element,and which forms the glass body gradually into a glass tube by contactingthe boring jig to the glass body, the boring jig is an electrode, andanother electrode is provided on an outer circumferential side of theglass body, or electrodes are provided on an inner circumferential sideand the outer circumferential side of the glass tube.

Furthermore, an apparatus for manufacturing a glass tube, which canachieve the object and which has a heating element disposed around acolumnar or a cylindrical glass member, and also has a boring jig to bebrought in contact with the glass body heated by said heating element,and which forms the glass body gradually into a glass tube by contactingthe boring jig to the glass body, further comprises at least one pair ofelectrodes provided on exteriors of both end surfaces in a longitudinaldirection of the glass body.

Further, preferably, the boring jig is surface-treated and at least apart of the boring jig, which makes contact with the glass body,contains one of silicon carbide, pyrocarbon, and metallic carbide.

Incidentally, in the case where the electrodes are provided on the innercircumferential side and the outer circumferential side of the glasstube, when the material of the heating element and the boring jig isgraphite, which is a conductive material, such a heating element and theboring jig can be utilized as electrodes. Further, preferably, thecontent of impurities other than graphite, which are contained in thegraphite of the boring jig, is equal to or less than 1 ppm.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic longitudinal sectional view illustrating a firsthigh purification apparatus available in a method of highly purifying aglass body according to a first embodiment of the invention;

FIGS. 2(a)-(b) are views illustrating the method of highly purifying aglass body according to the first embodiment of the invention;

FIG. 3 is a view illustrating another mode of the method of highlypurifying a glass body according to the first embodiment of theinvention;

FIG. 4 is a view illustrating another mode of the method of highlypurifying a glass body according to the first embodiment of theinvention;

FIGS. 5(a)-(b) are views illustrating another mode of the method ofhighly purifying a glass body according to the first embodiment of theinvention;

FIG. 6 is a schematic longitudinal sectional view illustrating a secondhigh purification apparatus available in a method of highly purifying aglass body according to a second embodiment of the invention;

FIG. 7 is a schematic longitudinal sectional view illustrating a thirdhigh purification apparatus available in methods of highly purifying aglass body according to modifications of a third embodiment and a fourthembodiment of the invention;

FIG. 8 is a schematic longitudinal sectional view illustrating a fourthhigh purification apparatus available in a method of highly purifying aglass body according to the third embodiment of the invention;

FIG. 9 is a view illustrating the method of highly purifying a glassbody according to the third embodiment of the invention;

FIG. 10 is a schematic longitudinal sectional view illustrating a fifthhigh purification apparatus available in a method of highly purifying aglass body according to the fourth third embodiment of the invention;

FIG. 11 is a schematic sectional view illustrating modifications of thethird embodiment and the fourth embodiment of the invention;

FIG. 12 is a view illustrating a method of highly purifying a glass pipeaccording to another embodiment of the invention;

FIG. 13 is a view illustrating a method of highly purifying a glass pipeaccording to another embodiment of the invention;

FIG. 14 is a schematic longitudinal sectional view illustrating a sixthhigh purification apparatus available in a method of highly purifying aglass body according to the fifth embodiment of the invention;

FIGS. 15(a)-(b) are views illustrating a method of highly purifying aglass body according to the fifth embodiment of the invention;

FIG. 16 is a schematic longitudinal sectional view illustrating aseventh high purification apparatus available in a method of highlypurifying a glass body according to a sixth embodiment of the invention;

FIG. 17 is a schematic view illustrating a manufacturing apparatus forperforming a method of manufacturing a glass tube according to a seventhembodiment of the invention;

FIG. 18 is a primary-part schematic view illustrating the vicinity of afurnace shown in FIG. 17;

FIG. 19 is a primary-part schematic view illustrating a modification ofthe apparatus according to the seventh embodiment;

FIG. 20 is a primary-part schematic view illustrating an apparatusaccording to an eighth embodiment of the invention;

FIG. 21 is a primary-part schematic view illustrating an apparatusaccording to a ninth embodiment of the invention;

FIG. 22 is a primary-part schematic view illustrating an apparatusaccording to a tenth embodiment of the invention;

FIG. 23 is a primary-part schematic view illustrating an apparatusaccording to an eleventh embodiment of the invention;

FIG. 24 is a schematic view illustrating an apparatus according to atwelfth embodiment of the invention; and

FIG. 25 is a primary-part schematic view illustrating an apparatus forperforming a conventional method of manufacturing a glass tube,

Incidentally, in the drawings, reference numerals 1 and 2 designateelectrodes, 11 a glass pipe, 11A a first end surface of a glass pipe,11B a second end surface of the glass pipe, 16 a glass rod, 101 and 101a an apparatus for manufacturing a glass tube, 103 a glass rod (theglass body), 104 a dummy pipe (the glass body) 106 a glass tube, 110 aninlet side base, 111 a first feed support pedestal, 112 a first chuck,120 an outlet side base, 121 a second feed support pedestal, 122 asecond chuck, 130 a boring jig, 131 a plug (an electrode), 132 a supportrod, 133 an electrode member (an electrode), 135 a securing member, 140,140 a, 140 b a heating furnace, 141 a heating member (an electrode), 142a coil, 143 and 145 spaces, 144 a muffle tube (an electrode), and 146 adie (an electrode).

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment)

A first embodiment of a method of highly purifying a glass bodyaccording to the invention is to apply voltages, in a nearly radialdirection of the glass body, to a cylindrical glass body (hereunderreferred to as a glass pipe) from a pair or plural pairs of electrodes,which are made to make contact with an outer circumferential surfaceside of the glass body, whereby impurities contained in the glass bodyare moved to the side of one of the electrodes according to a voltagegradient.

A high purification apparatus capable of performing a high purificationmethod according to this embodiment is described hereinbelow.

As illustrated in a schematic longitudinal sectional view of FIG. 1, afirst high purification apparatus 100 has an elongated base 21, heatingmeans 22 arranged at a specific distance along a longitudinal directionof the base 21 in such a way as to be able to surround the glass pipe11, and a power supply 51.

The base 21 is disposed in a state that the longitudinal direction ofthe base 21 is an approximately vertical direction. A first chuck 31enabled to grasp one end portion of the glass pipe 11 is attached to thebase 21 through a first support pedestal 32 above the heating means 22.A second chuck 41 enabled to grasp the other end portion of the glasspipe 11 is attached to the exterior of the base 21 through a secondsupport pedestal 42. The first chuck 31 and the second chuck 41 areconfigured in such a way as to be respectively rotated by motors (notshown) in synchronization with each other thereby to enable the glasspipe 11 to rotate around a central axis thereof, which is used as arotation axis.

Further, the second support pedestal 42 is configured in such a way asto be able to vertically move so as to facilitate attachment/detachmentof the glass pipe 11 to/from the first chuck 31 and the second chuck 41.

Furthermore, within the heating means 22, the pair of electrodes 1 and 2is provided and disposed in such a way as to sandwich the outercircumferential surface of the glass pipe 11. These electrodes 1 and 2each have a length that is comparable to the length of the heating means22 and that permits the electrodes 1 and 2 to make contact with theentire length in the longitudinal direction of an effective portion 11 aof the glass pipe 11. The electrodes 1 and 2 are supported by anelectrode support portion 3 that is installed on the base 21. Thiselectrode support portion 3 can move the electrodes 1 and 2 in such amanner as to allow the electrodes 1 and 2 to open and close in a radialdirection of the glass pipe 11, and as to cause the electrodes 1 and 2to make contact with the glass pipe 11 which is held by the first chuck31 and the second chuck 41 while the glass pipe 11 is interposed betweenthe electrodes 1 and 2. Moreover, a surface of each of the electrodes 1and 2, which is brought in contact with the glass pipe 11, has a curvedshape that has a curvature similar to the curvature of the outercircumferential surface of the glass pipe 11. Thus, a desired contactarea between the glass pipe and each of the electrodes 1 and 2 can beobtained.

The power supply 51 is usually a d. c. power supply. For example, anelectrically conductive wire drawn from a positive terminal is connectedto the electrode 2, while an electrically conductive wire drawn from anegative terminal is connected to the electrode 1. That is, theelectrode 2 is set to be an anode, while the electrode 1 is set to be acathode. Incidentally, the anode and the cathode may be conversely set.Graphite and surface-treated graphite may be cited as materials of theelectrodes 1 and 2. Especially, in view of the fact that the electrodes1 and 2 make contact with the glass pipe 11, preferably, surface-treatedgraphite is the material of the electrodes 1 and 2. Preferably,graphite, on the surface of which pyrocarbon (PyC), metal carbide (NbC,TaC, TiC, or ZrC), or silicon carbide (SiC) is provided, may be cited asa practical example of the surface-treated graphite. Impurities can beprevented from entering the glass pipe 11 from the electrodes 1 and 2 byusing such surface-treated graphite.

The heating means 22 has a cylindrical heating element. This heatingelement may be caused by, for example, a resistance heating method togenerate heat.

Further, the material of the heating element provided in the heatingmeans 22 may be exemplified by carbon or the like.

Incidentally, preferably, the content of impurities in carbon, such asgraphite, is equal to or less than 1 ppm. Thus, it is difficult forimpurities to enter the glass pipe 11.

Further, a gas pipe 84 enabled to communicate with a space in thegrasped glass pipe 11 is provided at, for example, the top portion 31Aof the first chuck. The gas pipe 84 is connected to an inner gas supplyapparatus 83 through a valve 82 enabled to conduct opening/closing of afluid passage. Furthermore, a gas pipe 63 enabled to communicate with aspace in the grasped glass pipe 11 is provided at, for instance, thebottom of the second chuck 41. The gas pipe 63 is connected to an intakepump 81 through a valve 61 enabled to conduct opening/closing of a fluidpassage.

Further, the first high purification apparatus 100 is provided with gasblowoff outlets 27 from which outer gas G2 is blown out from an upperpart of the base 21 to a lower part thereof.

Next, a method of highly purifying a glass pipe according to the firstembodiment of the invention, which uses the first high purificationapparatus 100 is described.

During a state in which the second chuck 41 and the heating means 22 aresufficiently away from each other, the top of the glass pipe (or silicaglass pipe) 11 is grasped by the first chuck 31. Incidentally, at thattime, the electrodes 1 and 2 are put into an open state by driving theelectrode support portion 3.

Meanwhile, the glass pipe 11 has the effective portion 11 a which is tobe performed high purification and dummy pipes 11 b connected to anupper part and a lower part of the effective portion 11 a. Portionsgrasped by the first chuck 31 and the second chuck 41 are dummy pipes 11b. The dummy pipes are usually low-purity low-end pipes and removed fromthe effective portion 11 a after completion of the high purification.The effective portion 11 a is set to have such a length that nearly theentire region thereof can be heated to a temperature, which is lowerthan 1300° C., by receiving heat from the heating means 22. Usually, thematerial of the effective portion 11 a is high-purity SiO₂ for opticalfibers, which contains 99.99% SiO₂ by weight or more. However, thematerial of the effective portion 11 a may contain additives, such asfluorine, boron, and germanium, for adjusting refraction index. In thiscase, the concentration of SiO₂ is lowered according to the quantity ofthese additives. Incidentally, it is assumed herein that these additivesare not included in a category of impurity cation described in thepresent specification.

Subsequently, the second support pedestal 42 is vertically moved towardthe heating means 22. The bottom of the glass pipe 11 is grasped by thesecond chuck 41. Then, the electrodes 1 and 2 are moved by the electrodesupport portion 3 toward the glass pipe 11, and brought into contactwith the glass pipe 11 while the electrodes 1 and 2 sandwich a part ofthe outer circumferential surface of the glass pipe 11, as illustratedin FIGS. 2(a)-(b).

Subsequently, the valve 82 is brought into a closed state, while thevalve 61 is put into an open state. Thus, the intake pump 81 isactivated to thereby evacuate the gas from an inner space of the glasspipe 11. Thereafter, the valve 82 is put into an open state, while thevalve 61 is brought into a closed state. Thus, the inner gas supplyapparatus 83 is activated to supply inner gas G1 to the inner space. Thevalve 82 is brought into a closed state when necessary. The inner gas G1is rare gas, such as argon gas, or nitrogen gas. It is preferable thatthe pressure of the inner gas G1 in the inner space of the glass pipe 11is set at −0.5 kPa·gage to −1.5 kPa·gage by adjusting an amount ofsupplied inner gas G1. More preferably, the pressure of the inner gas G1is positive. In this case, the pressure of the inner gas G1 is set at0.1 kPa·gage to 1.0 kPa·gage.

Subsequently, the heating means 22 is activated to heat the glass pipe11 at a temperature, which is less than 1300° C., and the power supply51 is activated to apply a voltage to the glass pipe 11 from theelectrodes 1 and 2, while the outer gas G2, which is rare gas, such asargon gas, or nitrogen gas, is made to flow from the gas blowoff outlet27 and from the upper part of the base 21 to the lower part thereof.Usually, the voltage is a d. c. voltage. Preferably, the voltage is setat a value within a range of 1 kV to 50 kV. It is preferable that theflow rate of the outer gas G2 is set at 10 l/min. to 20 l/min., and thatthe pressure of the outer gas G2 is set at 0.1 kPa·gage to 1.0 kPa·gage.Additionally, it is preferable that the pressure of the inner gas G1 isnearly equal to the pressure of the outer gas G2.

In this embodiment, as illustrated in FIGS. 2(a)-(b), the electrode 2serving as an anode and the electrode 1 serving as a cathode aredisposed in such a way as to face each other and as to make contact withthe exterior of the outer circumferential surface of the glass pipe 11.Thus, a voltage, by which the direction of the voltage gradient isalmost a radial direction of the glass pipe 11, is applied to the glasspipe 11. Further, the voltage gradient is negative in a direction from aside, with which the electrode 2 makes contact, to a side with which theelectrode 1 makes contact. Incidentally, the meaning of the expression“the direction of the voltage gradient is almost a radial direction ofthe glass pipe 11” includes that a voltage difference is generatedbetween the inner circumferential surface side and the outercircumferential surface of the glass pipe 11, and that a voltagedifference is generated in a direction of a diameter of the glass pipe11. In this embodiment, a voltage gradient is generated in a directionof a diameter of the glass pipe 11 between the electrodes 1 and 2.

FIGS. 2(a)-(b) show a sectional view in a radial direction of the glasspipe 11 in a state, in which the voltage gradient is generated, as aschematic view.

This voltage gradient causes impurity cations C (alkali metal ions, suchas lithium ions, sodium ions, and potassium ions, and copper ions)contained in the glass pipe 11 to move towards the outer circumferentialsurface side of the glass pipe 11, with which the electrode 1 serving asa cathode makes contact, as illustrated in FIG. 2(a).

Then, this application of the voltage is continued for a certain time.Thus, the impurity cations C contained in the glass pipe 11 can beconcentrated to the vicinity of a portion of the glass pipe, with whichthe electrode 1 makes contact, whereby the impurity cations C areunevenly distributed, as illustrated in FIG. 2(b).

At that time, preferably, the glass pipe 11 is heated and at least aportion of the glass pipe 11 to which the voltage is applied, namely,the effective portion 11 a has a temperature of less than 1300° C. Asthe temperature of the glass pipe 11 rises by heating the glass pipe 11,the diffusion coefficient of the impurity cation contained in the glasspipe 11 increases. This facilitates the movement of the cations in adirection in which the voltage gradient is negative.

In a state in which the heating temperature of the glass pipe 11 is low,the impurities are difficult to move into the glass pipe 11 from theelectrodes 1 and 2. Consequently, flexibility in selecting materialsused as those of the electrodes 1 and 2 is increased. Incidentally, itis necessary to set a processing time, in which the voltage is applied,to be long. In a case of some kind of the impurity cation, it isdifficult to move the impurity cation in the glass pipe 11.

In a state in which the heating temperature of the glass pipe 11 ishigh, the processing time, during which the voltage is applied, can bereduced. Incidentally, the glass pipe 11 becomes apt to deform.Moreover, in a case of some material of the electrodes 1 and 2, theimpurities are easily moved into the glass pipe 11. Therefore,preferably, the material, which can be used as that of the electrodes 1and 2, are, for example, the surface-treated graphite.

Preferably, the effective portion 11 a is heated and the temperaturethereof is equal to or higher than 450° C. More preferably, theeffective portion 11 a is heated and the temperature thereof is equal toor higher than 600° C. More preferably, the effective portion 11 a isheated and the temperature thereof is equal to or higher than 900° C. Inthe case that the temperature of the effective portion 11 a is equal toor higher than 450° C., the removing of alkali metal can easily beperformed. In the case that the temperature of the effective portion 11a is equal to or higher than 600 ° C., the removing of divalent metalions (Cu²⁺ and so on) can almost easily be performed. In the case thatthe temperature of the effective portion 11 a is equal to or higher than900° C., the removing of iron ions (Fe³⁺) and nickel ions (Ni²⁺) caneasily be performed.

Incidentally, when the glass pipe 11 is exposed to a temperatureexceeding 1300° C., the glass pipe 11 extremely deforms, whereby thenecessity for adding a postforming process for making the insidediameter and the outside diameter of the highly purified glass pipe 11constant in the longitudinal direction of the glass pipe 11 is extremelyincreased.

Therefore, the preferred lower limit value of the heating temperature ofthe glass pipe 11 is 450° C. or 600° C., while the preferred upper limitvalue thereof is less than 1300° C. (this is the same with embodimentsto be described later).

In a process in which the voltage is applied, preferably, the glass pipe11 is swung around a central axis thereof, which is used to as arotation axis, in a circumferential direction with respect to theelectrodes 1 and 2 by reversing a rotating direction of each of thefirst chuck 31 and the second chuck 41 at a short cycle while the firstchuck 31 and the second chuck 41 are rotated in synchronization witheach other. For example, the glass pipe 11 is swung whilehalf-circumference zones (zones partitioned by dashed lines X in FIG. 3)of the outer circumferential surface of the glass pipe 11 make contactwith the electrodes 1 and 2, respectively, as shown in this figure.Thus, the voltage can be evenly applied to the entire section in radialdirections of the glass pipe 11. Consequently, the movement of theimpurity cations can be effectively promoted. Moreover, the impuritycations can be unevenly distributed in a wide range in the vicinity ofthe outer circumferential surface of the glass pipe 11. Thus, theimpurity cations can be unevenly distributed in a shallow region closeto the outer circumferential surface of the glass pipe 11. Consequently,the highly purified region can effectively be increased.

Additionally, by swinging the glass pipe, heat received by the glasspipe 11 from the heating means 22 can be more uniformized in acircumferential direction of the glass pipe. Thus, deformation of theglass pipe 11, which occurs by unevenness of the temperaturedistribution in the circumferential direction of the glass pipe 11, canbe more surely reduced. Especially in a case that the heating means inthe high purification apparatus are partially provided in thecircumferential direction of the glass pipe, it is preferable to swingthe glass pipe.

Preferably, after completion of performing the process of applying thevoltage, a surface removing process of removing a portion of the glasspipe extending from the outer circumferential surface inward to apredetermined depth is performed. Thus, the impurity cations unevenlydistributed in the outer circumferential surface side portion of theglass pipe 11 can be removed, whereby the glass pipe, in which only thehighly purified portion remains, can be obtained. The surface removingprocess can be performed by utilizing grinding processing, chemicaletching processing using hydrofluoric acid, or flame polishing.

Preferred implementing conditions in the method of highly purifying aglass body (or glass pipe) according to the first embodiment describedhereinabove are shown below.

-   -   Outside diameter of the glass pipe: 120 mm    -   Inside diameter of the glass pipe: 10 mm to 15 mm    -   Length in a longitudinal direction of the glass pipe: 1200 mm    -   Temperature of the heating means: 1200° C.    -   Applied voltage: 40 kV    -   Voltage application processing time: 30 hours    -   Depth of the portion removed in the surface removing process        from the outer circumferential surface of the glass pipe: 1.5 mm    -   Width of (each one of) the electrodes: 48 mm.

The term “the width of the electrodes” designates the length of a partof the electrode, at which the electrode makes contact with the glassbody, to be measured tangentially and rectilinearly in a cross-sectionof the glass body, as illustrated in, for example, FIGS. 2(a)-(b).

The content concentration of the impurity cations contained in theeffective portion 11 a of the glass pipe 11, on which high purificationprocessing has been performed under such conditions, can be made to beequal to or less than 0.01 ppm by weight.

Also, examples of the relation among the heating temperature, theapplied voltage, and the processing time in the method of highlypurifying a glass body according to the first embodiment are shown inTable 1. TABLE 1 Heating Applied Processing Temperature Voltage Time (°C.) (kV) (h) Example 1 450 50 200 Example 2 600 45 80 Example 3 900 4050

In the case of Example 1 shown in Table 1, impurity alkali metal cationscan be moved. In the case of Example 2 shown in Table 1, in addition tothe alkali metal cations, metal ions, whose valency is equal to or lessthan 2, can be moved. In the case of Example 3, in addition to themovable impurity cations in the cases of Example 1 and Example 2, otherimpurity cations can be moved.

In the first high purification apparatus 100 shown in FIG. 1, thevoltage is applied to the glass pipe 11 by using the pair of electrodes1 and 2. In this case, preferably, the width of (each one of) theelectrodes ranges from 20% to 40% of the outside diameter of the glassbody.

Furthermore, in the apparatus, the voltage may be applied by providingplural pairs of electrodes therein. For example, as illustrated in aschematic view shown in FIG. 4, the apparatus may comprise three pairsof electrodes including electrodes 1 a, 1 b, and 1 c, which serve ascathodes, and electrodes 2 a, 2 b, and 2 c, which serve as anodes. Atthat time, the electrodes 1 a, 1 b, and 1 c are disposed in ahalf-circumference zone of the outer circumferential surface of theglass pipe 11. The electrodes 2 a, 2 b, and 2 c are disposed in theother half-circumference zone. In this case, preferably, the width of(each one of) the electrodes ranges from 10% to 30% of the outsidediameter of the glass body. Preferably, then, the voltages respectivelyapplied to the paired electrodes 1 a and 2 a, the paired electrodes 1 band 2 b, and the paired electrodes 1 c and 2 c are set. For instance, avoltage of 30 kV is applied to the electrodes 1 b and 2 b placed at thecenter, among the three pairs of electrodes. A voltage of 25 kV isapplied to the other electrodes, that is, the electrodes 1 a and 2 a,and the electrodes 1 c and 2 c. Consequently, the impurity cations canbe effectively moved to and around portion, at which the electrode 1 bmakes contact with the glass pipe, and unevenly distributed.

Further, as shown in FIG. 5, in the voltage application process,preferably, the glass pipe 11 is swung in the circumferential directionaround the central axis thereof used as a rotation axis with respect tothe electrodes 1 and 2, similarly as described with reference to FIG. 3.Consequently, the movement of the impurity cations can effectively bepromoted. Moreover, the impurity cations can be unevenly distributed ina wide range in the vicinity of the outer circumferential surface of theglass pipe 11.

Preferred implementing conditions in the method of highly purifying aglass body (or glass pipe) according to the embodiment described withreference to FIG. 4 are shown below.

-   -   Outside diameter of the glass pipe: 120 mm    -   Inside diameter of the glass pipe: 10 mm to 15 mm    -   Length in a longitudinal direction of the glass pipe: 1200 mm    -   Temperature of the heating means: 1100° C.    -   Applied voltage (to the electrodes 1 b and 2 b): 30 kV    -   Applied voltage (to the electrodes 1 a and 2 a and electrodes 1        c and 2 c): 25 kV    -   Voltage application processing time: 30 hours    -   Depth of the portion removed in the surface removing process        from the outer circumferential surface of the glass pipe: 1.5 mm    -   Width of (each one of) the electrodes: 36 mm.

The content concentration of the impurity cations contained in theeffective portion 11 a of the glass pipe 11, on which high purificationprocessing has been performed under such conditions, can be made to beequal to or less than 0.008 ppm by weight.

According to the method of highly purifying a glass body according tothe first embodiment of the invention described in the foregoingdescription, high purification can be performed by simultaneouslydecreasing deformation of a glass pipe. The postforming process formaking the inside diameter and the outside diameter of the glass pipeconstant in the longitudinal direction of the glass pipe (a process ofcutting partially or entirely the inner circumferential surface and theouter circumferential surface of the glass pipe or of reducing orincreasing partially or entirely the diameter thereof) can be omitted,and thereby the manufacturing cost of the highly purified glass pipe canextremely be reduced. Incidentally, the “cutting” referred to hereindesignates processing of a glass body to be performed by, for example, anumerically controlled lathe in such a way as to make the diameter ofthe glass body constant in the longitudinal direction of the glass body.Meanwhile, the surface removing process is a process of removing anouter circumferential surface portion having a predetermined depth froma glass pipe, which has been highly purified while deformation of theglass pipe has been decreased, by performing etching or cylindricalgrinding. This process is limited to a process of removing the portionhaving a predetermined depth, and extremely easy to perform, as comparedwith the postforming process to be performed due to the deformation ofthe glass pipe.

(Second Embodiment)

Although the aforementioned first embodiment of the method of highlypurifying a glass body is an embodiment adapted to simultaneously applyvoltages in the entire longitudinal direction of the effective portionof the glass pipe, a second embodiment of the method of highly purifyinga glass body according to the invention is adapted to serially applyvoltages, in a nearly radial direction of the glass pipe, to the glasspipe from electrodes put in contact with the outer circumferentialsurface side of the glass pipe.

As shown in a schematic longitudinal sectional view of FIG. 6, a secondhigh purification apparatus 200 is provided with heating means 23, whoselongitudinal length is set to be short, instead of the heating means 22of the first high purification apparatus 100. The high purificationapparatus 200 is also provided with electrodes 5 and 6, whose length isnearly equal to that of the heating means 23, instead of the electrodes1 and 2.

Also, the second high purification apparatus 200 has a first supportpedestal 35 and a second support pedestal 45, instead of the firstsupport pedestal 32 and the second support pedestal 42 of the first highpurification apparatus 100. The first support pedestal 35 and the secondsupport pedestal 45 each have a motor (not shown) and are configured insuch a manner as to be able to vertically move at predetermined speedsalong the base 21.

Next, a method of highly purifying a glass pipe according to the secondembodiment of the invention, which uses the second high purificationapparatus 200, is described mainly by citing the differences between thefirst embodiment and the second embodiment.

Similarly to the first embodiment, the end portions of the glass pipe 11are grasped by the first chuck 31 and the second chuck 41. The effectiveportion 11 a has a length in the longitudinal direction thereof, whichis sufficiently longer than the length in the longitudinal direction ofthe heating means 23, such that a partial region of the effectiveportion 11 a can be heated to a temperature, which is lower than 1300°C., by receiving heat from the heating means 23.

In the second embodiment, the glass pipe 11 is heated to a temperature,which is lower than 1300° C., by moving the first support pedestal 35and the second support pedestal 45 along the base 21 to thereby performrelative movement of the glass pipe 11 with respect to the heating means23. Moreover, the application of voltages in the nearly radial directioncan be performed on the entire glass pipe 11. Incidentally, the heatingmeans may be moved instead of the glass pipe 11.

Similarly to the fist embodiment, preferably, the second embodiment iscarried out by swinging the glass pipe 11 around the central axisthereof, which is used as a rotation axis, in the circumferentialdirection of the glass pipe 11 with respect to the electrodes 5 and 6.Also, the aforementioned surface evenly removing process may beperformed subsequently to the voltage application process.

According to the aforementioned second embodiment, advantages similar tothose of the first embodiment can be obtained.

Incidentally, preferably, a cooling means 7 is provided in the vicinityof an upper portion of the heating means 23, as illustrated in FIG. 6,and forcibly cools a portion of the glass pipe 11, which is heated bythe heating means 23 and also applied with a voltage, and in whichimpurity cations are unevenly distributed.

The cooling means may be means for blowing out cooling gas, such asinactive gas and cooling air, to the glass pipe 11, or alternatively,may be a cooling jacket (not shown) adapted to cover the periphery ofthe glass pipe 11. Preferably, the cooling is performed and thetemperature of a cooled portion of the glass pipe 11 is equal to or lessthan 800° C. or less than 500° C.

The cooling is forcibly performed to lower the temperature to a value atwhich the diffusion coefficient of the impurity cations is sufficientlow and it is difficult to move the impurity cations. Consequently, theimpurity cations can be made to remain unevenly distributed to the outercircumferential portion of the glass pipe, before the unevenlydistributed impurity cations are diffused in the glass pipe 11immediately after the impurity cations are unevenly distributed to theglass pipe 11. Therefore, advantages of the method of highly purifying aglass body according to the invention can maximally be obtained.

Incidentally, in the description of the first and second embodiments,the cylindrical glass pipe has been described as an example of the glassbody, on which the high purification processing is performed. However, aglass body shaped like a column (hereunder referred to as a glass rod)may be employed as an object on which the high purification processingis performed. In this case, the high purification of the glass rod canbe performed by using an apparatus and a method, which are similar tothe apparatus and the method used for highly purifying the glass pipe.Incidentally, there is no need for using inner gas to be fed on theinner side of the glass pipe.

As illustrated in FIG. 7, a third high purification apparatus 100 asuitably used for highly purifying a glass rod is obtained by removingconstituent elements, which are employed for using the inner gas G1,from the first high purification apparatus 100 shown in FIG. 1.

The glass rod 16 is configured by respectively connecting dummy rods 16b to the top and the bottom of the effective portion 16 a to be highlypurified. The material of the effective portion 16 a is similar to thatof the effective portion 11 a of the aforementioned glass pipe 11. Thematerial of the dummy rods 16 b is similar to that of the dummy pipes 11b of the aforementioned glass pipe 11.

Further, the third high purification apparatus 100 a shown in FIG. 7 isused in the case where voltages are simultaneously applied in the entirelongitudinal direction of the effective portion 16 a. However, thisapparatus may employ a method of sequentially applying nearly diametralvoltages to the glass rod 16 in the longitudinal direction of the glassrod 16. For example, as described with reference to FIG. 6, highpurification can be performed on the glass rod 16, similarly to the caseof serially applying nearly diametral voltages to the glass pipe 11 inthe longitudinal direction of the glass pipe 11.

Further, the glass rod is a solid glass body, differently from the glasspipe in which a space has been formed. Thus, as compared with the glasspipe, it is hard for thermal deformation to occur in the glass rod.Consequently, an upper limit to the heating temperature at highpurification can be set to be higher than that in the case of highpurification of the glass pipe. A preferred upper limit value of theheating temperature is 1450° C.

For instance, in the case that high purification is performed on theglass rod under conditions nearly similar to those for Example 1 toExample 2 (see Table 1) described in the description of the firstembodiment, a processing time is 24 hours when the heating temperatureis 1400° C. and the applied voltage is 40 kV. Thus, impurity cationssimilar to those in the case of Example 3 can be moved.

(Third Embodiment)

A third embodiment of the method of highly purifying a glass bodyaccording to the invention is to apply a voltage, in a nearly radialdirection of a glass pipe, to the glass pipe from electrodes disposed onthe outer circumferential side of the glass pipe and to move impuritiescontained in the glass body toward the outer circumferential side ortoward the inner circumferential side by utilizing the gradient of thevoltage.

As shown in a schematic longitudinal sectional view of FIG. 8, a fourthhigh purification apparatus 300 has an elongated base 21, heating means22 arranged at a specific distance along a longitudinal direction of thebase 21 in such a way as to be able to surround a glass pipe 11, and apower supply 51. The base 21 is disposed in a state that thelongitudinal direction of the base 21 is an approximately verticaldirection. A first chuck 31 enabled to grasp one end portion of theglass pipe 11 is attached to the base 21 through a first supportpedestal 32 above the heating means 22. A second chuck 41 enabled tograsp the other end portion of the glass pipe 11 is attached to theexterior of the base 21 through a second support pedestal 42 below theheating means 22. The first chuck 31 and the second chuck 41 areconfigured in such a manner as to be respectively rotated by motors (notshown) in synchronization with each other thereby to enable the glasspipe 11 to rotate around a central axis thereof, which is used as arotation axis.

Further, the second support pedestal 42 is configured in such a manneras to be able to vertically move so as to facilitateattachment/detachment of the glass pipe 11 to/from the first chuck 31and the second chuck 41.

An electrode fixing member 33 is attached above the first chuck 31. Anelongate inner electrode 12 is grasped by the electrode fixing member 33through an electrically conductive electrode connecting portion 14penetrating through a top portion 31A of the first chuck. Incidentally,the inner electrode 12 is configured in such a way as to downwardlyvertically extend to the vicinity of the bottom of the heating means 22.The inner electrode 12 is set to have a maximum outside diameter in atransverse section thereof which is smaller than an inside diameter ofthe glass pipe 11 on which high purification processing is performed.The inner electrode 12 is configured in such a way as to not makecontact with the glass pipe 11.

Further, a gas pipe 84 enabled to communicate with a space in thegrasped glass pipe 11 is provided at, for example, the top portion 31Aof the first chuck. The gas pipe 84 is connected to an inner gas supplyapparatus 83 through a valve 82 enabled to conduct opening/closing of afluid passage. Moreover, a gas pipe 63 enabled to communicate with aspace in the grasped glass pipe 11 is provided at, for instance, thebottom of the second chuck 41. The gas pipe 63 is connected to an intakepump 81 through a valve 61 enabled to conduct opening/closing of a fluidpassage.

The power supply 51 is usually a d. c. power supply. For example, anelectrically conductive wire drawn from a positive terminal is connectedto the electrode connecting portion 14. The aforementioned graphite andsurface-treated graphite can be cited as materials of the innerelectrode 12 and the electrode connecting portion 14. Especially,preferably, surface-treated graphite is the material of the innerelectrode 12.

On the other hand, an electrically conductive wire drawn from thenegative terminal of the power supply 51 is connected to a heatingelement of the heating means 22. The material of the heating element canbe preferably exemplified by carbon or the like.

Incidentally, preferably, the content of impurities of carbon, such asgraphite, is equal to or less than 1 ppm. Consequently, it becomes hardfor impurities to enter the glass pipe 11.

Further, the fourth high purification apparatus 300 is provided with gasblowoff outlets 27 from which outer gas G2 is blown out from an upperpart of the base 21 to a lower part thereof.

Next, a method of highly purifying a glass pipe according to the thirdembodiment of the invention, which uses the fourth high purificationapparatus 300 is described.

During a state in which the second chuck 41 and the heating means 22 aresufficiently away from each other, the top of the glass pipe (or silicaglass pipe) 11 is grasped by the first chuck 31 and the inner electrode12 is accommodated in the inner space of the glass pipe 11.

Incidentally, the glass pipe 11 is similar to that described in thedescription of the first embodiment.

Subsequently, the second support pedestal 42 is vertically moved towardthe heating means 22. The bottom of the glass pipe 11 is grasped by thesecond chuck 41. In this case, the central axis of the glass pipe almostcoincides with that of the inner electrode 12. The glass pipe 11 ismounted in such a way as not to make contact with the inner electrode12.

Subsequently, the valve 82 is brought into a closed state, while thevalve 61 is put into an open state. Thus, the intake pump 81 isactivated to thereby evacuate the gas from an inner space of the glasspipe 11. Thereafter, the valve 82 is put into an open state, while thevalve 61 is brought into a closed state. Thus, the inner gas supplyapparatus 83 is activated to supply inner gas G1 to the inner space. Thevalve 82 is brought into a closed state when necessary. The inner gas G1is rare gas, such as argon gas, or nitrogen gas. It is preferable thatthe pressure of the inner gas G1 in the inner space of the glass pipe 11is set at −0.5 kPa·gage to −1.5 kPa·gage by adjusting an amount ofsupplied inner gas G1. Alternatively, preferably, the pressure of theinner gas G1 is positive. In this case, the pressure of the inner gas G1is set at 0.1 kPa·gage to 1.0 kPa·gage.

Subsequently, a voltage application process is performed by activatingthe heating means 22 to heat the glass pipe 11 at a temperature, whichis less than 1300° C., and activating the power supply 51 to apply avoltage to the glass pipe 11 from the electrodes 1 and 2 while the outergas G2, which is rare gas such as argon gas, or nitrogen gas, is made toflow from the gas blowoff outlet 27 and from the upper part of the base21 to the lower part thereof. Usually, the voltage is a d. c. voltage.Preferably, the voltage is set at a value within a range of 1 kV to 50kV. It is preferable that the flow rate of the outer gas G2 is set at 10l/min. to 20 l/min., and that the pressure of the outer gas G2 is set at0.5 kPa·gage to 1.5 kPa·gage.

In this embodiment, the electrode 12 serving as an anode and the heatingmeans 22 serving as a cathode are disposed on the interior and theexterior of the glass pipe 11 in such a way as to face each other. Theinner gas G1 intervenes between the inner electrode 12 and the glasspipe 11, while the outer gas G2 intervenes between the cathode and theglass pipe 11. Consequently, a voltage, by which the direction of thevoltage gradient is almost a radial direction of the glass pipe 11, isapplied to the glass pipe 11. Further, the voltage gradient is negativein a direction from the inner circumferential surface side of the glasspipe 11 to the outer circumferential surface side. Incidentally, in thisembodiment, the case, in which the direction of the voltage gradient isalmost a radial direction of the glass pipe 11, includes a case in whichthe direction of the voltage gradient is slightly deviated from theradial direction of the glass pipe 11 due to, for instance, thedeviation of the inner electrode 12 from the central axis of the glasspipe 11.

Consequently, the impurity cations C contained in the glass pipe 11 tomove in a direction of the outer circumferential surface side of theglass pipe 11, as illustrated in FIG. 9(a), which is a sectional view ofa primary part of the apparatus shown in FIG. 8.

Then, the voltage application process is continued for a certain time.Thus, the impurity cations C contained in the glass pipe 11 can bediffused from the outer circumferential surface of the glass pipe 11 andevacuated from the first high purification apparatus 100 by utilizingthe flow of the outer gas G2, or can be unevenly distributed in thevicinity of the outer circumferential surface of the glass pipe 11, asillustrated in a primary-part sectional view of FIG. 9(b).

Furthermore, as described above, it is preferable that the glass pipe 11is heated at a temperature that is less than 1300° C.

In this embodiment, the voltage application process is performed whilethe glass pipe 11 is rotated around the central axis thereof, which isused as a rotation axis, at a rotational speed, which is within a rangeof 1 rpm to 100 rpm, by rotating the first chuck 31 and the second chuck41 in synchronization with each other. Incidentally, this case isassumed to include a case where the central axis of the glass pipe 11 issomewhat deviated from the rotation axis.

Heat received by the glass pipe 11 from the heating means 22 can be moreuniformized in the circumferential direction thereof by setting therotation speed to be equal to or more than 1 rpm. Thus, deformation ofthe glass pipe 11, which occurs by unevenness of the temperaturedistribution in the circumferential direction thereof, can be moreeffectively reduced. Especially in a case that the heating means in thehigh purification apparatus are not continuously provided in thecircumferential direction of the glass pipe, it is preferable that theglass pipe is rotated at a rotational speed, which is within theaforementioned range.

On the other hand, deformation of the glass pipe 11, which occurs by acentrifugal force, can be effectively decreased by setting therotational speed to be equal to or less than 100 rpm. Especially,preferably, when the rotational speed is set to be equal or less than 20rpm, the deformation of the glass pipe 11, which occurs by a centrifugalforce, can be more surely decreased.

After completion of the voltage application process, a surfaceevenly-removing process of evenly removing a portion of the glass pipe11 extending from the outer circumferential surface inward to apredetermined depth may be performed when necessary. Consequently, thehigh purification of the glass pipe 11 can be more surely performed.

Preferred implementing conditions in the method of highly purifying aglass pipe according to the third embodiment are shown below.

-   -   Outside diameter of the glass pipe: 75 mm to 150 mm    -   Inside diameter of the glass pipe: 52.5 mm to 105 mm    -   Length in a longitudinal direction of the glass pipe: 1000 mm to        1500 mm    -   Voltage application processing time: 20 hours to 30 hours    -   Depth of the portion removed in the surface removing process        from the outer circumferential surface of the glass pipe: 0.1 mm        to 0.3 mm.

According to the method of highly purifying a glass body according tothe third embodiment of the invention described in the foregoingdescription, high purification can be performed by simultaneouslydecreasing deformation of a glass pipe. The postforming process formaking the inside diameter and the outside diameter of the glass pipeconstant in the longitudinal direction thereof (a process of cuttingpartially or entirely the inner circumferential surface and the outercircumferential surface of the glass pipe or of reducing or increasingpartially or entirely the diameter thereof) can be omitted. Thus, themanufacturing cost of the highly purified glass pipe can extremely bereduced. Incidentally, the surface evenly-removing process to be addedwhen needed is a process of removing an outer circumferential surfaceportion having a predetermined depth from the circumferential surface ofa glass pipe, which is highly purified while deformation thereof isdecreased. This process is limited to a process of evenly removing theportion having a predetermined depth, and extremely easy to perform, ascompared with the postforming process to be performed due to thedeformation thereof. Incidentally, the electrodes may be adapted to bebrought into contact with the glass pipe.

(Fourth Embodiment)

As shown in a schematic longitudinal sectional view of FIG. 10, a fifthhigh purification apparatus 400 is provided with heating means 23, whoselongitudinal length is set to be short, instead of the heating means 22of the fourth high purification apparatus 300. The high purificationapparatus 400 is also provided with an inner electrode 13, whose lengthis nearly equal to that of the heating means 23, instead of the innerelectrode 12.

Also, the fifth high purification apparatus 400 has a first supportpedestal 35 and a second support pedestal 45, instead of the firstsupport pedestal 32 and the second support pedestal 42 of the fourthhigh purification apparatus 300. The first support pedestal 35 and thesecond support pedestal 45 each have a motor (not shown) and areconfigured in such a manner as to be able to vertically move atpredetermined speeds along the base 21.

Next, a method of highly purifying a glass pipe according to the fourthembodiment of the invention, which uses the fifth high purificationapparatus 400, is described mainly by citing the differences between thethird embodiment and the fifth embodiment.

Similarly to the third embodiment, end portions of the glass pipe (orsilica glass pipe) 11 are grasped by the first chuck 31 and the secondchuck 41 and the inner electrode 13 is accommodated in the inner spaceof the glass pipe 11. The effective portion 11 a has a length in thelongitudinal direction thereof, which is sufficiently longer than thelength in the longitudinal direction of the heating means 23, and apartial region of the effective portion 11 a can be heated to atemperature, which is lower than 1300° C., by receiving heat from theheating means 23.

In the fourth embodiment, the glass pipe 11 is heated to a temperature,which is lower than 1300° C., by moving the first support pedestal 35and the second support pedestal 45 along the base 21 to thereby performrelative movement of the glass pipe 11 with respect to the heating means23. Moreover, the application of voltages in the nearly radial directioncan be performed on the entire glass pipe 11. Incidentally, the heatingmeans may be moved instead of the glass pipe 11.

Further, in this embodiment, preferably, after the application of thevoltage, the glass pipe 11 is cooled down by using the cooling means 7illustrated in FIG. 6.

Similarly to the third embodiment, in the fourth embodiment, the voltageapplication process is performed while the glass pipe 11 is rotatedaround the central axis thereof, which is used as a rotation axis, at arotational speed which is within a range of 1 rpm to 100 rpm.Incidentally, the surface removing process may be performed after thevoltage application process.

According to the aforementioned fourth embodiment, advantages similar tothose of the third embodiment can be obtained.

In the third embodiment and the fourth embodiment, although the heatingmeans 22 and 23 are not connected to the power supply, as illustrated ina schematic sectional view of FIG. 11, instead, an outer electrode 15 tobe connected to the power supply may additionally be disposed betweenthe outer circumferential surface of the glass pipe 11 and each of theheating means 22 and 23.

Further, although the inner electrode is used as an anode and the outerelectrode or the heating means is used as a cathode in the thirdembodiment and the fourth embodiment, another embodiment using the innerelectrode as a cathode and also using the outer electrode or the heatingmeans as an anode can be exemplified.

In this case, similarly to the third and fourth embodiments, a voltage,by which the direction of the voltage gradient is almost a radialdirection of the glass pipe 11, is applied to the glass pipe 11.Further, the voltage gradient is negative in a direction from the outercircumferential surface side of the glass pipe 11 to the innercircumferential surface side.

Consequently, impurity cations C (alkali metal ions, such as lithiumions, sodium ions, and potassium ions, and copper ions) contained in theglass pipe move in a direction of the inner circumferential surface sideof the glass pipe.

Thus, the high purification of a glass pipe can be more surely conductedby performing the surface removing process of removing a portion of theglass pipe extending from the inner circumferential surface to apredetermined depth.

Furthermore, although in third and fourth embodiments, the inner spaceof the glass pipe 11 is filled with the inner gas, while the outer gasis made to flow, the embodiments may be modified so that the inner gasis made to flow in the inner space of the glass pipe and the outer gasis made to flow in the base.

Further, although an embodiment using the inner gas G1 and the outer gasG2 in the voltage application process is exemplified in the descriptionof the aforementioned embodiment, the method of high purification of aglass pipe according to the invention is not limited thereto.

For example, an embodiment is adapted so that the inner electrode isslide-contacted with the inner circumferential surface of the glasspipe, which rotates around the central axis to be used as a rotationaxis. In this adaptation, this is done without using the inner gas G1.Another embodiment is adapted so that the outer electrode isslide-contacted with the outer circumferential surface of the glasspipe, which rotates around the central axis to be used as a rotationaxis. In this adaptation, this is done without using the outer gas G2.Also, another embodiment is obtained by combining the foregoingembodiments with each other (see FIG. 12, in this case, the inner gas G1and the outer gas G2 are unnecessary). The above-mentionedsurface-treated graphite is preferably exemplified for the electrode tobe slide-contacted with the glass pipe, so as to surely decrease themovement of the impurities from the electrode to the glass pipe.

Further, although the heating means 22 and 23 are not connected to thepower supply as illustrated in a schematic sectional view of FIG. 13,instead, the outer electrode 15, which is connected to the power supplyand slide-contacted with the outer circumferential surface of the glasspipe 11, may additionally be disposed between the outer circumferentialsurface of the glass pipe 11 and each of the heating means 22 and 23.

Preferred implementing conditions in the method of highly purifying aglass body (or glass pipe) according to the embodiment shown in FIG. 12are shown below.

-   -   Outside diameter of the glass pipe: 150 mm    -   Inside diameter of the glass pipe: 10 mm to 15 mm    -   Length in a longitudinal direction of the glass pipe: 1500 mm    -   Temperature of the heating means: 1100° C.    -   Applied Voltage: 30 kV    -   Voltage application processing time: 30 hours    -   Depth of the portion removed in the surface evenly-removing        process from the outer circumferential surface of the glass        pipe: 1.5 mm.

The content concentration of the impurity cations contained in theeffective portion 11 a of the glass pipe 11, on which high purificationprocessing is performed under such conditions, can be made to be equalto or less than 0.010 ppm by weight.

(Fifth Embodiment)

As shown in a schematic longitudinal sectional view of FIG. 14, a sixthhigh purification apparatus 500 has an elongated base 71, heating means25 arranged at a specific distance along a longitudinal direction of thebase 71 in such a way as to be able to surround a glass pipe 11, and apower supply 52. The base 71 is disposed in a state that thelongitudinal direction thereof is an approximately vertical direction. Afirst chuck 36 enabled to grasp one end portion of the glass pipe 11 isattached to the base 71 through a first support pedestal 37 above theheating means 25. A second chuck 46 enabled to grasp the other endportion of the glass pipe 11 is attached to the base 71 through a secondsupport pedestal 42 below the heating means 25. A second electrode 66 isprovided in the second chuck 46 in such a way as to be able to makecontact with an end surface of the glass pipe 11.

The first chuck 36 and the second chuck 46 each have a motor (not shown)and rotated in synchronization with each other thereby to enable theglass pipe 11 to rotate around a central axis thereof, which is used asa rotation axis.

The power supply 52 is usually a d. c. power supply. An electricallyconductive wire drawn from a positive terminal is connected to a firstelectrode 65. On the other hand, an electrically conductive wire drawnfrom the negative terminal of the power supply 52 is connected to asecond electrode 66. As the materials of the first electrode 65 and thesecond electrode 66, graphite and the above-mentioned surface-treatedgraphite can be cited.

Next, the fifth embodiment of the method of highly purifying a glasspipe according to the invention, which uses the sixth high purificationapparatus 500 is described.

First, a glass pipe 11 having an end, to which a dummy pipe 19 isfusion-connected so that the central axes of the pipes are aligned, isprepared.

An end portion of the glass pipe 11, which is provided at the side ofthe dummy pipe 19, is grasped by the second chuck 46, while the otherend portion thereof is grasped by the first chuck 36. Incidentally, afirst end surface 11A of the glass pipe (an end surface opposite to thedummy pipe) and a second end surface 11B (an end surface provided at thedummy-pipe side) of the glass pipe make contact with the first electrode65 and the second electrode 66, respectively. Further, the length in thelongitudinal direction of the glass pipe 11 is set at a value, at whichnearly the entire region of the glass pipe 11 receives heat from theheating means 25 and can be heated to a temperature of less than 1300°C.

Subsequently, a voltage application process is performed by activatingthe heating means 25 to heat the glass pipe 11 at a temperature, whichis less than 1300° C., and activating the power supply 52 to apply avoltage to the glass pipe 11. Usually, the voltage is a d. c. voltage.Preferably, the voltage is set at a value within a range of 1 kV to 50kV.

In this embodiment, the first electrode 65 serving as an anode and theelectrode 66 serving as a cathode are respectively disposed at both endsof the glass pipe 11 in such a way as to face each other. Thus, avoltage, by which the direction of the voltage gradient is almost adirection of the central axis of the glass pipe 11 (a longitudinaldirection), is applied to the glass pipe 11.

Further, the voltage gradient is negative in a direction from a firstend surface 11A of the glass pipe to a second end surface 11B thereof.

Consequently, impurity cations C (alkali metal ions, such as lithiumions, sodium ions, and potassium ions, and copper ions) contained in theglass pipe move in a direction of the second end surface 11B of theglass pipe, as shown in FIG. 15(a), which is a sectional view of aprimary part of the apparatus shown in FIG. 14.

Then, the voltage application process is continued for a certain time.Thus, the impurity cations C contained in the glass pipe 11 can beunevenly distributed by the dummy pipe 19, as illustrated in FIG. 15(b).

After completion of the voltage application process, an end portionremoving process of removing a portion of the glass pipe extending fromthe second end surface 11B inward to a predetermined depth can beperformed when necessary. In the fifth embodiment, the end portionremoving process can easily be performed by removing the dummy pipe 19from the glass pipe 11. Consequently, the high purification of the glasspipe 11 can be more surely performed.

Preferred implementing conditions in the method of highly purifying aglass pipe according to the fifth embodiment are shown below.

-   -   Outside diameter of the glass pipe: 40 mm to 75 mm    -   Inside diameter of the glass pipe: 28 mm to 52.5 mm    -   Length in a longitudinal direction of the glass pipe (including        the dummy pipe): 1000 mm to 1500 mm    -   Length in a longitudinal direction of the dummy pipe: 50 mm to        100 mm    -   Voltage application processing time: 20 hours to 30 hours.

Similarly to the third embodiment, in the fifth embodiment, the voltageapplication process is performed while the glass pipe 11 is rotatedaround the central axis thereof, which is used as a rotation axis, at arotational speed, which is within a range of 1 rpm to 100 rpm. Morepreferably, the rotational speed is set to be equal to or more than 1rpm and equal to or less than 20 rpm.

According to the aforementioned fifth embodiment, advantages similar tothose of the third embodiment can be obtained.

(Sixth Embodiment)

As shown in a schematic longitudinal sectional view of FIG. 16, aseventh high purification apparatus 600 is provided with heating means26, whose longitudinal length is set to be short, instead of the heatingmeans 25 of the sixth high purification apparatus 500. The highpurification apparatus 600 has a first support pedestal 39 and a secondsupport pedestal 49, instead of the first support pedestal 37 and thesecond support pedestal 47 of the sixth high purification apparatus 500.The first support pedestal 39 and the second support pedestal 49 eachhave a motor (not shown) and are configured in such a manner as to beable to vertically move at predetermined speeds along the base 71.Incidentally, the heating means may be moved instead of the glass pipe11.

Next, a method of highly purifying a glass pipe according to the sixthembodiment of the invention, which uses the seventh high purificationapparatus 600, is described mainly by citing the differences between thefifth embodiment and the sixth embodiment.

Similarly to the fifth embodiment, an end portion of the glass pipe 11is grasped by the first chuck 36 and the second chuck 46. The glass pipe11 has a length in the longitudinal direction thereof, which issufficiently longer than the length in the longitudinal direction of theheating means 26, such that a partial region of the glass pipe 11 can beheated to a temperature, which is lower than 1300° C., by receiving heatfrom the heating means 26.

In the sixth embodiment, a voltage application process of heating theglass pipe 11 to a temperature, which is lower than 1300° C., by movingthe first support pedestal 39 and the second support pedestal 49 alongthe base 71 to thereby perform relative movement of the glass pipe 11with respect to the heating means 26, and simultaneously applying avoltage to the glass pipe 11 can be performed on the entire glass pipe11.

Similarly to the fifth embodiment, impurity cations contained in theglass pipe 11 move toward the second end surface 11B of the glass pipe.Thus, preferably, first, the first chuck 36 and the heating means areplaced to be adjacent with each other. The voltage application processis performed on the top portion of the glass pipe 11. Then, the relativemovement of the glass pipe 11 and the heating means 26 is performed.Thus, the voltage application process is performed on a lower region ofthe glass pipe 11. Consequently, the impurity cations contained in theglass pipe 11 can be unevenly and efficiently distributed in the dummypipe 19.

Further, in this embodiment, preferably, after the application of thevoltage, the glass pipe 11 is cooled down by using the cooling means 7illustrated in FIG. 6.

Similarly to the third embodiment, in the sixth embodiment, the voltageapplication process is performed while the glass pipe 11 is rotatedaround the central axis thereof, which is used as a rotation axis, at arotational speed, which is within a range of 1 rpm to 100 rpm. Morepreferably, the rotation speed is set to be equal to or more than 5 rpmand equal to or less than 100 rpm. Further, when necessary, the endportion removing process may be performed after the voltage applicationprocess. In the sixth embodiment, the end portion removing process caneasily be performed by removing the dummy pipe 19 from the glass pipe11. Consequently, the high purification of the glass pipe 11 can be moresurely performed.

According to the aforementioned second embodiment, advantages similar tothose of the first embodiment can be obtained.

Further, in the fifth and sixth embodiments, a columnar glass rod may beused, instead of using the glass pipe 11. In this case, the highpurification of the glass rod can be performed by using an apparatus anda method, which are similar to the apparatus and the method used in thecase of the high purification of the glass pipe 11. Incidentally, apreferred upper limit value of the heating temperature is 1450° C.

Incidentally, preferably, in the glass body to be used according to theinvention, the length of the effective portion is less than 500 mm inthe case of applying a voltage in the longitudinal direction (thedirection of the central axis) of the glass body. In the case of movingthe impurity cations in the longitudinal direction of the glass body,whose effective portion has a length being equal to or more than 500 mm,the moved distance of the cation is long. Thus, a time required toperform the high purification processing is long. Moreover, thenecessity for increasing a voltage to be applied arises. When theapplied voltage is too high (for instance, exceeds 50 kV), there is afear that a discharge may occur before the voltage is applied to theglass body.

In contrast, in the case of applying the voltage in a nearly radialdirection of the glass body, the effective portion is permitted to havea length that is equal to or more than 500 nm. Therefore, in the case ofhigh purification of a glass body, whose effective portion has a largelength, the application of a voltage in a nearly radial direction of theglass body is more efficient in performing the high purificationthereof.

Further, a high-purity glass body, whose outside diameter is equal to ormore than 100 mm, highly purified by such a method is a relatively largeglass body. Preferably, the high purification is performed to obtain thecontent concentration of the impurity cations contained in the effectiveportion of the glass pipe being equal to or less than 0.010 ppm byweight. Preferably, the content concentration of each of the impuritycations (alkali metal ions, such as lithium ions, sodium ions, andpotassium ions, and copper ions) contained in the effective portion ofthe glass pipe is equal to or less than 10 ppb by weight.

The use of such a high precision and large-sized high purity glass bodyas an optical fiber base material ingot enables the efficientmanufacture of high-quality optical fibers that show favorabletransmission characteristics.

Hereinafter, modes, which can be employed as a method of highlypurifying a glass pipe, are briefly described.

{circumflex over (1)} A method of highly purifying a glass pipe, whichhas a voltage application process of applying a voltage to a glass pipewhile heating the glass pipe to a temperature, which is within a rangeof temperature that is equal to or higher than 1000° C. and less than1300° C.

{circumflex over (2)} A method of highly purifying a glass pipeaccording to the item {circumflex over (1)}, wherein the voltageapplication process is performed while the glass pipe is rotated aroundthe central axis, which is used as a rotation axis, at a rotationalspeed that is within a range of 1 rpm to 100 rpm.

{circumflex over (3)} A method of highly purifying a glass pipeaccording to the item {circumflex over (1)} or {circumflex over (2)},wherein a direction of a voltage gradient of the voltage is almost aradial direction of the glass pipe.

{circumflex over (4)} A method of highly purifying a glass pipeaccording to the item {circumflex over (3)}, which has a surfaceevenly-removing process of removing a portion of the glass pipeextending from an outer circumferential surface inward to apredetermined depth subsequently to the voltage application process,wherein the voltage gradient is a negative gradient in a direction fromthe inner circumferential surface side to the outer circumferentialsurface side of the glass pipe.

{circumflex over (5)} A method of highly purifying a glass pipeaccording to the item {circumflex over (3)}, which has a surfaceevenly-removing process of removing a portion of the glass pipeextending from an inner circumferential surface inward to apredetermined depth subsequently to the voltage application process,wherein the voltage gradient is a negative gradient in a direction fromthe outer circumferential surface side to the inner circumferentialsurface side of the glass pipe.

{circumflex over (6)} A method of highly purifying a glass pipeaccording to the item {circumflex over (1)} or {circumflex over (2)}, inwhich the direction of the voltage gradient of the voltage is adirection of the central axis of the glass pipe.

{circumflex over (7)} A method of highly purifying a glass pipeaccording to the item {circumflex over (5)}, which has an end portionremoving process of removing a portion of the glass pipe extending froma second end surface inward to a predetermined depth, wherein thevoltage gradient is a negative gradient in a direction from a first endsurface of the glass pipe to the second end surface of the glass pipe.

EXAMPLE 1

High purification of a glass pipe according to the third embodiment isperformed under the following conditions by using the high purificationapparatus pursuant to the fourth high purification apparatus 300.

-   -   Outside diameter of the glass pipe: 150 mm    -   Inside diameter of the glass pipe: 105 mm    -   Length in the longitudinal direction of the glass pipe: 1500 mm.

The composition of the glass pipe is SiO₂ containing 0.1 ppm by weightof impurity cations (alkali metal ions, such as lithium ions, sodiumions, and potassium ions, and copper ions).

Incidentally, the concentration of impurity cations is the content ofthe impurity cations with respect to the entire glass pipe. In thefollowing description, the concentration of impurity cations has thesame meaning.

Further, change in the outside diameter in the longitudinal direction ofthe glass pipe is measured by an ultrasonic measuring apparatus. Then, astandard deviation (hereunder also referred to as a glass pipe diameterstandard deviation) is calculated. The standard deviation is 0.1 mm.

-   -   Inner gas: argon, −0.5 kPa·gage    -   Outer gas: argon, 10 l/min., 1 kPa·gage    -   Heating temperature: 1100° C.    -   Voltage: a d. c. voltage of 40 kV    -   Voltage Application process time: 30 hours    -   Rotational speed of the glass pipe: 30 rpm    -   Depth of the glass pipe removed in the surface evenly-removing        process (chemical etching) from the outer circumferential        surface of the glass pipe: 0.24 mm.

EXAMPLE 2

Method of highly purifying a glass pipe is performed, similarly toExample 1, except that the heating temperature is 1280° C.

COMPARATIVE EXAMPLE 1

Method of highly purifying a glass pipe is performed, similarly toExample 1, except that the heating temperature is 1320° C.

The following table shows resultant glass pipes obtained aftercompletion of performing the high purification methods according to theExamples and the Comparative Example. TABLE 2 Concentration of GlassPipe Heating Impurity Standard Temperature Cations Deviation (° C.)(weight · ppm) (mm) Example 1 1100 0.02 0.1 Example 2 1280 <0.01 0.3Comparative 1320 <0.01 0.8 Example 1

As shown in Table 2, according to the high purification method in thecase of the Examples in which the heating temperature is set to be lessthan 1300° C., the impurity cations are decreased. Moreover, theglass-pipe-diameter standard deviation hardly changes. That is, the highpurification is performed while decreasing deformation of the glass pipeat a high degree. The glass pipes purified at a high degree by the highpurification methods in the case of the Examples meet the shape accuracyand purity for optical fibers without any other processing.

On the other hand, in the case of Comparative Example 1, theglass-pipe-diameter standard deviation increases. This means thatdeformation of the glass pipe has occurred. Thus, the glass pipe in thecase of Comparative Example 1 does not meet, for example, the shapeaccuracy for optical fibers without any other processing.

Meanwhile, high purity glass tubes can be manufactured by performingboring (including increasing a diameter) of a glass body whileappropriately utilizing the aforementioned methods of highly purifying aglass body.

Next, embodiments of a method and an apparatus for manufacturing a glasstube including highly purification according to the invention aredescribed with reference to FIGS. 17 to 24.

(Seventh Embodiment)

A seventh embodiment herein described is an embodiment adapted togenerate a voltage gradient in a radial direction of a gradually formedglass tube by utilizing, when a boring jig is brought in contact with aglass body, a heating element and the boring jig as electrodes, andapplying voltages to an inner circumferential side and an outercircumferential side of the glass tube. Incidentally, the radialdirection of the glass tube designates a direction perpendicular to thelongitudinal direction of the glass tube.

As shown in FIG. 17, an apparatus 101 of manufacturing glass tubes,which is used in this embodiment, manufactures glass tubes by performingwhat is called a piercing method. The apparatus 101 is provided with afurnace 140 for heating a glass rod 103, an inlet side base 110 disposedat an inlet side of the furnace 140, and an outlet side base 120disposed at an outlet side of the furnace 140.

A glass dummy pipe 104 is connected to an end of the glass rod 103 to bebored.

A first feed support pedestal 111 enabled to slide-move at a desiredspeed in a lateral direction, as viewed in this figure, is provided onan inlet side base 110. In this first feed support pedestal 111 a boringtermination end side of the glass rod 103 is grasped by the first chuck112, and the glass rode 103 can be rotated around an axis extending inthe longitudinal direction.

Also, a second feed support pedestal 121 enabled to slide-movelaterally, as viewed in this figure, similarly as the first feed supportpedestal does is provided on an outlet side base 120. The travelingspeed of the second feed support pedestal 121 is appropriatelycontrolled in such a way as to be associated with that of the first feedsupport pedestal 111. In this second feed support pedestal 121, an endof the dummy pipe 104 connected to a boring initiation end side of theglass rod 103 is grasped by a second chuck 122, and the glass rod 103can be rotated around a longitudinal axis thereof. Further, the rotationthereof can be controlled in such a manner as to be synchronized withthe rotation of the first chuck 112 of the first feed support pedestal111. Furthermore, the rotational speed of the first chuck 112 and therotational speed of the second chuck 122 may be made to differ from eachother. Preferably, the rotational speeds of the first chuck 112 and thesecond chuck 122 are about 1 rpm to 100 rpm.

A fixing member 135 for fixing the boring jig 130 is provided on theoutlet side base 120. The boring jig 130 has a support rod 132 and aplug 131 provided at an end of the support rod 132, which is connectedto the fixing member 135. Furthermore, the support rod 132 has a centralaxis, which is the same as that of the plug 131, and is supported in astate that the central axis thereof coincides with the central axis ofthe glass rod 103.

The plug 131 is available at the softening temperature of the glass rod103 and formed of a material that does not chemically react with theglass rod 103. Preferably, the plug 131 is formed of graphite. Graphiteexcels in stability even at a high temperature, at which glass issoftened, and has a high degree of electrical conductivity.

Further, the content of impurities contained in ordinary graphite isabout 400 ppm. However, preferably, high purity graphite is used as thematerial of the plug 131 of this embodiment. More preferably, thecontent of impurities contained in this graphite is equal to or lessthan 1 ppm. Thus, when the plug 131 is brought into contact with andpressed into the glass rod 103, the impurities are difficult to moveinto the glass rod 103 from the plug 131.

Further, preferably, the plug 131 is surface-treated and at least a partof the plug 131, which makes contact with glass, contains one of siliconcarbide (SiC), pyrocarbon (PyC), and metallic carbide. Incidentally, themetallic carbide is, for example, niobium carbide (NbC), tantalumcarbide (TaC), titanium carbide (TiC), zircon carbide (ZrC) exemplifypreferred materials thereof.

A surface treatment is, for example, to form a coating layer, which ismade of silicon carbide described above, on the plug 131 thereby enhancestrength and abrasion resistance thereof and prevent oxidization thereofin a high temperature condition. Moreover, such surface treatmentenables the plug 131 to maintain the high purity of the surface thereof.Furthermore, such surface treatment prevents the diffusion of impuritiesfrom the inside of the plug 131 to the glass rod 103.

Further, the furnace 140 of this embodiment is of the high frequencydielectric heating type. The heating element 141 generates heat byfeeding a. c. current in a coil 142. The heating element 141 is acylindrical graphite one covering the surroundings of an abuttingportion at which the plug 131 abuts against the glass rod 103. Thisheating element 141 generates heat at a temperature, which is equal toor higher than the softening temperature of glass, thereby to heat andsoften the glass rod 103.

Incidentally, the softening point of the high purity glass body producedby VAD method or the like is about 1700° C.

Next, the constitute elements for applying a voltage to the innercircumferential side and the outer circumferential side of a glass tubegradually formed are described.

The heating element 141 and the plug 131 are configured in such a way asto serve as electrodes respectively polarized to positive or negativepotentials as shown in FIG. 18. That is, a d. c. power supply isconnected to the heating element 141 and the plug 131.

With such a configuration, the plug 131 can apply a voltage to the innercircumferential side of the glass tube 106 by making contact with thebored glass tube 106. Further, the heating element 141 can apply avoltage to the outer circumferential side of the glass tube 106.Preferably, a gas supply means (not shown) communicating with the insideof a space 143 is provided thereby to supply gas to the inside of thespace 143. The electrical conductivity between the heating element 141and the glass tube 106, which are in a noncontact state, is enhanced bythis gas. Thus, voltages can efficiently be applied to the glass tube106.

Further, a rare gas, such as argon gas, or nitrogen gas may be used assuch gas. Furthermore, preferably, ionized gas is used.

When a glass tube is manufactured in this embodiment, the glass rod 103fed into the furnace 140 is heated and softened by causing the heatingelement 141 to generate heat, as illustrated in FIGS. 17 and 18. Theplug 131 of the boring jig 130 is brought into contact with and pressedinto a softened portion. Thus, the glass rod 103 is gradually bored tothereby gradually form the glass tube 106. Then, when the plug 131 ispressed into the glass rod 103, voltages are applied from the heatingelement 141 and the plug 131 to the gradually formed glass tube 106. Atthat time, the heating element 141 and the plug 131 are set in such away as to respectively serve electrodes whose potentials differ fromeach other. Consequently, a voltage gradient in a radial direction ofthe glass tube 106 can be generated.

For example, as illustrated in FIG. 18, the heating element 141 is setto be a cathode, while the plug 131 is set to be an anode. The voltagegradient generated in this case is a negative gradient according towhich the potential changes from a positive one to a negative one towardthe outer circumferential side from the inner circumferential side ofthe glass tube 106.

The impurities moved into the glass body 103 from the plug 131 at themanufacture thereof are mainly alkali metal ions, such as lithium ions,sodium ions, and potassium ions, alkaline earth metal ions, such ascalcium ions, and cations, such as copper ions. Therefore, the voltagegradient generated in a radial direction of the softened glass tube 106causes the impurities to move to the outer circumferential portion ofthe glass tube 106 placed at a cathode side.

Thus, high purification of portions of the glass tube 106, which areother than the outer circumferential portion, can be achieved by movingthe impurities, which have been included into the glass tube 106, to theouter circumferential portion thereof.

The lower the viscosity of the softened glass, the more likely it isthat the movement of the impurities occurs. According to the invention,high purification is performed nearly simultaneously with boring. Thus,the bored glass tube 106 is heated to a temperature of, for example,about 1800° C. Thus, the impurities can efficiently be moved, wherebythe high purification can effectively be performed.

Further, the impurities localized in the glass tube 106 canappropriately be eliminated by removing an outer circumferential portionof the glass tube 106 to a desired depth through the use of mechanicalmeans, such as grinding, and chemical means, such as etching processingusing hydrofluoric acid.

Further, in the mode shown in FIG. 18, a space 143 is provided betweenthe heating element 141 and the glass tube 106, and the heating element141, which serves as an electrode, and the glass tube 106 is in anoncontact state. However, the heating element 141 and the glass tube106 may be brought into contact with each other. That is, the insidediameter of the heating element 141 is set to make contact with theouter circumferential surface of the bored glass tube 106 at the innercircumferential surface of the heating element 141, as illustrated inFIG. 19. With such a configuration, a voltage can be applied directly tothe glass tube 106, which is being bored and increases in the outsidediameter, from both the outer circumferential side and the innercircumferential side without using gas. High purification caneffectively be performed. Additionally, there is no need for providing agas supply means in the apparatus.

Further, in a case where the inside diameter of the heating element 141is set to be equal to the outside diameter of the glass tube 106, theglass tube 106 can be formed to have the outside diameter of

a desired value.

Further, in this case, the impurities can be prevented by performingsurface treatment on the heating element 141 similarly to the plug 131from being moved into the glass tube 106.

Incidentally, although a mode, in which the impurities are localized atthe outer circumferential side of the glass tube, has been described inthe description of this embodiment, the impurities may be localized atthe inner circumferential side. That is, the heating element 141 is usedas an anode, while the plug 131 is used as a cathode. A voltage gradientgenerated in this case is a negative gradient, according to which thepotential changes from a positive one to a negative one, from the outercircumferential side of the glass tube 106 to the inner circumferentialside thereof.

In a case where the plug 131 is used as a cathode, the impurities, whichare cations, tends to remain in the plug 131. Thus, the impurities canbe prevented from being moved into the glass tube 106 from the plug 131.Further, the impurities have been moved into the glass body 103 can belocalized in the inner circumferential portion of the glass tube 106 andalso can be absorbed into the plug 131.

Thus, even in the case that the impurities are localized in the innercircumferential portion of the glass tube 106, the inner circumferentialportion can be removed to a desired depth when needed. Consequently, theimpurities can be removed from the glass tube 106.

Further, preferably, restoration of the plug 131 having absorbed theimpurities is performed. For example, the restoration of the plug 131 isperformed by heating the plug 131 through the use of a furnace, whoseheating space is in the atmosphere of chlorine gas, and then diffusingthe impurity cations contained in the plug 131 into the chlorine gas.

In the foregoing description, the embodiment utilizing the heatingelement and the boring jig as the electrodes has been described.However, according to the invention, other members can be used as theelectrodes. Such an embodiment is described hereinbelow.

(Eighth Embodiment)

In the description of this eighth embodiment, an embodiment utilizing anelectrode member provided in the boring jig as an electrode isdescribed.

The configuration of an apparatus for manufacturing a glass tube, whichis employed by this embodiment, is almost similar to that of theapparatus for manufacturing a glass tube, which is shown in FIG. 17. Aprimary part of this embodiment is described with reference to FIG. 20.

As shown in FIG. 20, a boring jig 130 a used in this embodiment isprovided with an electrode member 133 serving as an electrode in therear and vicinity (at the right side, as viewed in this figure) of aplug 131. This electrode member 133 is shaped like a cylinder and fixedto a support rod 132. The outside diameter thereof is nearly equal tothat of the plug 131. The material thereof is similar to that of theplug 131. Preferably, a surface treatment, which is similar to thatperformed on the plug 131, is performed on this electrode member.

In this embodiment, a d. c. power supply is connected to this electrodemember 133, instead of connecting the d. c. power supply to the plug131. Thus, the electrode member 133 can apply a voltage to the innercircumferential side of the glass tube 106 by making contact with abored glass tube 106.

The electrode member 133 of such a configuration has the function of anelectrode and acts in such a manner as to maintain the inside diameterof the softened glass tube 106. Further, in a case where a coating layermade of silicon carbide or the like is formed on a surface of theelectrode member 133, impurities is not moved into the glass rod 106.

When the plug 131 is pressed into the glass rod 103, voltages areapplied from the heating element 141 and the electrode member 133 to thegradually formed glass tube 106. At that time, the heating element 141and the electrode member 133 are set in such a way as to serve aselectrodes that differ in potential from each other. Consequently, avoltage gradient can be generated in a radial direction of the glasstube 106.

In a case where the heating element 141 is a cathode and the electrodemember 133 is an anode, as illustrated in FIG. 20, a negative voltagegradient, according to which the potential changes from a positive valueto a negative value in a direction from the inner circumferential sideof the glass tube 106 to the outer circumferential side thereof, isgenerated. In this case, impurities are localized in an outercircumferential portion of the glass tube 106.

Further, conversely to the case illustrated in FIG. 20, the heatingelement 141 and the electrode member 133 can be set to be an anode and acathode, respectively. In this case, impurities are localized in aninner circumferential portion of the glass tube 106.

Incidentally, when the electrode member 133 is used as a cathode, thevoltage may also be applied to the plug 131 and then the plug 131 mayserve as a cathode. In this case, impurities are absorbed by the plug131. Thus, preferably, the plug 131 is constituted by a nonconductivematerial. Alternatively, preferably, a part of a support rod 132 locatedbetween the electrode member 133 and the plug 131 is constituted by anonconductive material. Boron nitride, zirconia, ceramics and so on canbe used as the nonconductive material.

Consequently, since impurities can be absorbed only by the electrodemember 133, the plug 131 is not contaminated by impurities. Preferably,the contaminated electrode member 133 is detached from the support rod132 and replaced with a new member, alternatively, restored. Thisfacilitates the maintenance of the apparatus.

Additionally, this embodiment may be configured by setting the outsidediameter of the electrode member 133 to be smaller than that of the plug131 thereby to detach the electrode member 133 from the innercircumferential surface of the glass tube 106. In this case, preferably,the aforementioned gas is supplied to the inside of the glass tube 106.

Further, similarly to the seventh embodiment, the heating element 141 isbrought into contact with the glass tube 106 in the eighth embodiment,as illustrated in FIG. 19.

(Ninth Embodiment)

In the description of this ninth embodiment, an embodiment utilizing amuffle tube provided in a furnace as an electrode is described.

As illustrated in FIG. 21, a furnace 140 a used in this embodiment has acylindrical muffle tube 144 provided in a space at the innercircumferential side of the heating element 141. A space 145 is providedbetween this muffle tube 144 and the glass tube 106 to be formed.Further, carbon or the like may be used as the material of the muffletube 144.

In this embodiment, a d. c. power supply is connected to this muffletube 144, instead of connecting a d. c. power supply to the heatingelement 141. Thus, the muffle tube 144 can apply a voltage to the outercircumferential side of the glass tube 106. Further, preferably, gas issupplied to the inside of the space 145 when the voltage is applied tothe glass tube 106.

With such a configuration, the muffle tube 144 and the plug 131 areutilized as electrodes, and a voltage gradient can be generated in aradial direction of the glass tube 106.

Therefore, similarly to the case of the seventh embodiment, the glasstube 106 to be formed can be highly purified. Further, when the muffletube 144 is contaminated, the muffle tube 144 is replaced or restored,and thereby the maintenance of the apparatus is easy to perform.

(Tenth Embodiment)

In the description of this tenth embodiment, an embodiment utilizing adie provided in a furnace as an electrode is described.

As illustrated in FIG. 22, a furnace 140 b used in this embodiment has adie 146 provided on the inner circumferential surface of the heatingelement 141. This die 146 is made of graphite constituted in such a wayas to prevent impurities from being moved into a glass tube 106,similarly to the aforementioned plug 131. In this embodiment, a d. c.power supply is directly connected to the die 146, instead of theheating element 141. Thus, the die 146 and the plug 131 are utilized aselectrodes, and a voltage gradient can be generated in a radialdirection of the glass tube 106.

At that time, the die 146 and the plug 131 are brought into contact withthe glass tube 106, and thus voltages can efficiently act on the glasstube 106, without using gas, differently from the aforementionedembodiment using gas. Additionally, there is no need for providing gassupply means in the apparatus.

Further, the provision of the die 146 enables that the glass tube 106can be formed in such a way as to have a desired outside diameter whilethe glass rod 103 is bored by the plug 131.

Therefore, the glass tube 106 can be formed with high accuracy, and alsocan efficiently be highly purified.

(Eleventh Embodiment)

In the description of this eleventh embodiment, an embodiment, in whichvoltages are applied to a glass tube from at least one pair ofelectrodes provided on the outer circumferential surface of the glasstube, is described.

As shown in FIG. 23, an apparatus for manufacturing a glass tube to beused in this embodiment has a pair of electrodes 1 and 2, which areprovided in a furnace 140 a and disposed in such a way as to face eachother and as to sandwich the outer circumferential surface of the glasstube 106. These electrodes 1 and 2 are formed of the same material asthat of the electrodes 1 and 2 described in the foregoing description ofthe high purification method. The surface of each of the electrodes,which makes contact with the glass tube 106, has a shape curved at acurvature, which is nearly equal to that of the outer circumferentialsurface of the glass tube 106. In this embodiment, the electrodes areused in a manner similar to the manner, in which the electrodes are usedin, for example, the first embodiment or the second embodiment describedby referring to FIGS. 2 to 5. That is, high purification of a glass tubecan be performed by unevenly distributing impurities, which arecontained in the glass tube, in a part of the outer circumferentialsurface thereof, while glass tubes are manufactured.

(Twelfth Embodiment)

In the description of this twelfth embodiment, an embodiment, in whichvoltages are applied to a glass body from electrodes disposed by makingcontact with a first end surface and a second end surface in thelongitudinal direction of the glass body, is described.

As illustrated in FIG. 24, an apparatus 101 a of manufacturing a glasstube, which is used in this embodiment, electrodes 65 and 66 areprovided on the exteriors of both end surfaces in the longitudinaldirection of the glass body consisting of a glass rod 103 and a dummypipe 104, similarly to the sixth high purification apparatus 500 (seeFIG. 14) described in the description of the fifth embodiment. Theconfiguration of each of these electrodes 65 and 66 is almost similar tothat in the case of the fifth embodiment. Also, the method of usingthese electrodes is similar to that in the case of the fifth embodiment.That is, when boring is performed by a boring jig 130, a voltage isapplied in the longitudinal direction of the glass tube 106, a voltagegradient in the longitudinal direction thereof is generated.Consequently, impurities are unevenly distributed in a cathode sideportion, and high purification of a glass tube can be performed whilethe glass tube is manufactured.

Further, in all the aforementioned embodiments, it does not matterwhether or not the electrodes make contact with the glass body (or theglass tube). In the case that the electrodes make contact therewith,there is no necessity for using gas. Preferably, at least an edge orperipheral portion of a portion, with which the cathode makes contact,is removed. In the case that the electrodes do not make contacttherewith, at least an edge or peripheral portion at the side, at whichthe cathode is placed, that is, at the side at which the voltagegradient is low, is removed. Further, in the aforementioned seventh totwelfth embodiments, the high purification method and apparatus canappropriately use the configurations of the methods and apparatusesdescribed in the description of the aforementioned first to sixthembodiments.

Incidentally, although the modes, in each of which boring is performedon the glass rod that is a columnar glass body, have been described inthe description of the seventh to twelfth embodiments, the method ofmanufacturing a glass tube according to the invention can be employedeven in a case of increasing the inside diameter of a glass pipe, whichis a cylindrical glass body.

Further, although the induction heating furnace is cited as an exampleof a furnace, a resistance heating furnace may be used.

Although the invention has been described in detail with reference tospecific embodiments, it is obvious to those skilled in the art thatvarious changes and modifications can be made without departing from thespirit and scope thereof.

This application is based on Japanese Patent Application No.2002-235274, filed on Aug. 12, 2002, Japanese Patent Application No.2002-234563, filed on Aug. 12, 2002, and Japanese Patent Application No.2003-166430, filed on Jun. 11, 2003, the content of which isincorporated herein by reference.

Industrial Applicability

As is apparent form the foregoing description of the embodiment,according to the invention, there can be provided a method of highlypurifying a glass body, which enables high purification thereof whiledecreasing deformation of the glass body at a high degree, a highlypurified glass body, and a method and an apparatus for manufacturing aglass tube, which can obtain a highly purified glass tube.

1. A method of highly purifying a glass body, the method comprising:applying voltages, in a nearly radial direction of said glass body, toat least a part in a longitudinal direction of a columnar or cylindricalglass body from at least one pair of electrodes placed on an exterior ofan outer circumferential surface of the glass body.
 2. The method ofhighly purifying a glass body according to claim 1, wherein saidelectrodes are plural anodes and plural cathodes arranged in acircumferential direction of said glass body, and wherein a potential ofeach of said anodes and a potential of each of said cathodes arerespectively set.
 3. The method of highly purifying a glass bodyaccording to claim 1, wherein a relative swinging motion between saidglass body and each of said electrodes occurs in a circumferentialdirection of said glass body.
 4. The method of highly purifying a glassbody according to claim 1, further comprising: a surface removingprocess of removing a portion of the glass body extending from the outercircumferential surface inward to a predetermined depth after thevoltages are applied to the glass body.
 5. The method of highlypurifying a glass body according to claim 1, wherein the voltages aresimultaneously applied to an entirety in a longitudinal direction of aneffective portion of said glass body.
 6. The method of highly purifyinga glass body according to claim 1, wherein the voltages are seriallyapplied to said glass body in a longitudinal direction of the glassbody.
 7. The method of highly purifying a glass body according to claim6, wherein while the voltages are serially applied to said glass body ina longitudinal direction of the glass body, portions, to which thevoltages have been applied, are sequentially cooled.
 8. The method ofhighly purifying a glass body according to claim 1, wherein a length inthe longitudinal direction of said effective portion of said glass bodyis equal to or more than 500 mm.
 9. A method of highly purifying a glassbody the method comprising: when a cylindrical glass body is rotatedaround a central axis thereof used as a rotation axis at a rotationalspeed, which is equal to or more than 1 rpm and equal to or less than100 rpm, applying voltages, in a nearly radial direction of said glassbody, to at least a part in a longitudinal direction of said glass bodyfrom electrodes disposed at an outer circumferential surface side and aninner circumferential surface side of said glass body.
 10. The method ofhighly purifying a glass body according to claim 9, wherein the voltagesare applied while said cylindrical glass body is rotated around thecentral axis to be used as a rotation axis at a rotational speed, whichis equal to or more than 1 rpm and equal to or less than 20 rpm.
 11. Themethod of highly purifying a glass body according to claim 9, furthercomprising: a surface removing process of removing a portion of theglass body extending from an outer circumferential surface inward to apredetermined depth after the voltages are applied to the glass body,wherein a voltage gradient of the voltage is set to be a negativegradient in a direction from the inner circumferential side of saidglass body to the outer circumferential side thereof.
 12. The method ofhighly purifying a glass body according to claim 9, further comprising:a surface removing process of removing a portion of the glass bodyextending from an inner circumferential surface outward to apredetermined depth after the voltages are applied to the glass body,wherein a voltage gradient of the voltage is set to be a negativegradient in a direction from the outer circumferential side of saidglass body to the inner circumferential side thereof.
 13. The method ofhighly purifying a glass body according to claim 9, wherein the voltagesare simultaneously applied to an entirety in a longitudinal direction ofan effective portion of said glass body.
 14. The method of highlypurifying a glass body according to claim 9, wherein the voltages areserially applied to said glass body in a longitudinal direction of theglass body.
 15. The method of highly purifying a glass body according toclaim 14, wherein while the voltages are serially applied to said glassbody in a longitudinal direction of the glass body, portions, to whichthe voltages have been applied, are sequentially cooled.
 16. The methodof highly purifying a glass body according to claim to 9, wherein alength in the longitudinal direction of said effective portion of saidglass body is equal to or more than 500 mm.
 17. A method of highlypurifying a glass body, the method comprising: applying voltages in alongitudinal direction of a columnar or cylindrical glass body fromelectrodes placed on exteriors of a first end surface and a second endsurface in a longitudinal direction of said glass body.
 18. The methodof highly purifying a glass body according to claim 17, furthercomprising: an end portion removing process of removing a portion of theglass body extending from the second end surface of said glass body tothe first end surface to a predetermined depth wherein a voltagegradient of the voltage is set to be a negative gradient in a directionfrom the first end surface to the second end surface of said glass body.19. The method of highly purifying a glass body according to claim 17,wherein a length in a longitudinal direction of an effective portion ofsaid glass body is less than 500 mm.
 20. The method of highly purifyinga glass body according to claim 18 or 19, wherein the voltages areapplied while heating a portion of said glass body, to which thevoltages are applied, to a temperature that is equal to or higher than450° C. The method of highly purifying a glass body according to claim1, wherein the voltages are applied without bringing said electrodes incontact with said glass body.
 21. The method of highly purifying a glassbody according to claim 9, wherein the voltages are applied withoutbringing said electrodes in contact with said glass body.
 22. The methodof highly purifying a glass body according to claim 17, wherein thevoltages are applied without bringing said electrodes in contact withsaid glass body.
 23. The method of highly purifying a glass bodyaccording to claim 1, wherein the voltages are applied in a state inwhich at least a part of said electrodes is brought into contact withsaid glass body.
 24. The method of highly purifying a glass bodyaccording to claim 9, wherein the voltages are applied in a state inwhich at least a part of said electrodes is brought into contact withsaid glass body.
 25. The method of highly purifying a glass bodyaccording to claim 17, wherein the voltages are applied in a state inwhich at least a part of said electrodes is brought into contact withsaid glass body.
 26. The method of highly purifying a glass bodyaccording to claim 1, wherein the voltages are applied while heating aportion of said columnar glass body, to which the voltages are applied,to a temperature that is less than 1450° C.
 27. The method of highlypurifying a glass body according to claim 17, wherein the voltages areapplied while heating a portion of said columnar glass body, to whichthe voltages are applied, to a temperature that is less than 1450° C.28. The method of highly purifying a glass body according to claim 1,wherein the voltages are applied while heating a portion of said glassbody, to which the voltages are applied, to a temperature that is lessthan 1300° C.
 29. The method of highly purifying a glass body accordingto claim 9, wherein the voltages are applied while heating a portion ofsaid glass body, to which the voltages are applied, to a temperaturethat is less than 1300° C.
 30. The method of highly purifying a glassbody according to claim 17, wherein the voltages are applied whileheating a portion of said glass body, to which the voltages are applied,to a temperature that is less than 1300° C.
 31. The method of highlypurifying a glass body according to claim 26, wherein the voltages areapplied while heating a portion of said glass body, to which thevoltages are applied, to a temperature that is equal to or higher than450° C.
 32. The method of highly purifying a glass body according toclaim 27, wherein the voltages are applied while heating a portion ofsaid glass body, to which the voltages are applied, to a temperaturethat is equal to or higher than 450° C.
 33. The method of highlypurifying a glass body according to claim 28, wherein the voltages areapplied while heating a portion of said glass body, to which thevoltages are applied, to a temperature that is equal to or higher than450° C.
 34. The method of highly purifying a glass body according toclaim 29, wherein the voltages are applied while heating a portion ofsaid glass body, to which the voltages are applied, to a temperaturethat is equal to or higher than 450° C.
 35. The method of highlypurifying a glass body according to claim 30, wherein the voltages areapplied while heating a portion of said glass body, to which thevoltages are applied, to a temperature that is equal to or higher than450° C.
 36. The method of highly purifying a glass body according claim26, wherein the voltages are applied while heating a portion of saidglass body, to which the voltages are applied, to a temperature that isequal to or higher than 600° C.
 37. The method of highly purifying aglass body according to claim 27, wherein the voltages are applied whileheating a portion of said glass body, to which the voltages are applied,to a temperature that is equal to or higher than 600° C.
 38. The methodof highly purifying a glass body according to claim 28, wherein thevoltages are applied while heating a portion of said glass body, towhich the voltages are applied, to a temperature that is equal to orhigher than 600° C.
 39. The method of highly purifying a glass bodyaccording to claim 29, wherein the voltages are applied while heating aportion of said glass body, to which the voltages are applied, to atemperature that is equal to or higher than 600° C.
 40. The method ofhighly purifying a glass body according to claim 30, wherein thevoltages are applied while heating a portion of said glass body, towhich the voltages are applied, to a temperature that is equal to orhigher than 600° C.
 41. The method of highly purifying a glass bodyaccording to claim 26, wherein the voltages are applied while heating aportion of said glass body, to which the voltages are applied, to atemperature that is equal to or higher than 900° C.
 42. The method ofhighly purifying a glass body according to claim 27, wherein thevoltages are applied while heating a portion of said glass body, towhich the voltages are applied, to a temperature that is equal to orhigher than 900° C.
 43. The method of highly purifying a glass bodyaccording to claim 28, wherein the voltages are applied while heating aportion of said glass body, to which the voltages are applied, to atemperature that is equal to or higher than 900° C.
 44. The method ofhighly purifying a glass body according to claim 29, wherein thevoltages are applied while heating a portion of said glass body, towhich the voltages are applied, to a temperature that is equal to orhigher than 900° C.
 45. The method of highly purifying a glass bodyaccording to claim 30, wherein the voltages are applied while heating aportion of said glass body, to which the voltages are applied, to atemperature that is equal to or higher than 900° C.
 46. The method ofhighly purifying a glass body according to claim 1, wherein a contentconcentration of impurity cations contained in an effective portion ofsaid glass body is decreased to equal to or less than 0.01 ppm byweight.
 47. The method of highly purifying a glass body according toclaim 9, wherein a content concentration of impurity cations containedin an effective portion of said glass body is decreased to equal to orless than 0.01 ppm by weight.
 48. The method of highly purifying a glassbody according to claim 17, wherein a content concentration of impuritycations contained in an effective portion of said glass body isdecreased to equal to or less than 0.01 ppm by weight.
 49. A high purityglass body highly purified by the method of highly purifying a glassbody according to claim 1, wherein an outside diameter of the glass bodyis equal to or more than 100 mm, and wherein a length of an effectiveportion is equal to or more than 500 mm.
 50. A high purity glass bodyhighly purified by the method of highly purifying a glass body accordingto claim 9, wherein an outside diameter of the glass body is equal to ormore than 100 mm, and wherein a length of an effective portion is equalto or more than 500 mm.
 51. A high purity glass body highly purified bythe method of highly purifying a glass body according to claim 17,wherein an outside diameter of the glass body is equal to or more than100 mm, and wherein a length of an effective portion is less than 500mm.
 52. The high purity glass body according to claim 49, wherein acontent concentration of impurity cations contained in an effectiveportion of said glass body is equal to or less than 0.01 ppm by weight.53. The high purity glass body according to claim 50, wherein a contentconcentration of impurity cations contained in an effective portion ofsaid glass body is equal to or less than 0.01 ppm by weight.
 54. Thehigh purity glass body according to claim 51, wherein a contentconcentration of impurity cations contained in an effective portion ofsaid glass body is equal to or less than 0.01 ppm by weight.
 55. Amethod of manufacturing a glass tube by heating a columnar orcylindrical glass body to thereby soften said glass body, and thenbringing a boring jig in contact with the softened portion of said glassbody to thereby gradually form said glass body into a glass tube, themethod comprising: when said boring jig is brought into contact withsaid glass body, applying voltages, in a nearly radial direction of saidglass body, to said glass tube from at least one pair of electrodesprovided on an exterior of an outer circumferential surface of saidglass body to thereby generate a voltage gradient.
 56. The method ofmanufacturing a glass tube according to claim 55, further comprising:after said glass tube is formed, removing at least a peripheral portionof said glass tube at which the voltage gradient is set to be low.
 57. Amethod of manufacturing a glass tube by heating a columnar orcylindrical glass body to thereby soften said glass body, and thenbringing a boring jig in contact with the softened portion of said glassbody to thereby gradually form said glass body into a glass tube, themethod comprising: when said boring jig is brought into contact withsaid glass body, applying voltages between said boring jig and an outercircumferential side of said glass body or between an innercircumferential side and an outer circumferential side of said glasstube to thereby generate a voltage gradient in a nearly radial directionof said glass body or said glass tube.
 58. The method of manufacturing aglass tube according to claim 57, further comprising: after said glasstube is formed, removing at least a peripheral portion of said glasstube at which the voltage gradient is set to be low.
 59. A method ofmanufacturing a glass tube by heating a columnar or cylindrical glassbody to thereby soften said glass body, and then bringing a boring jigin contact with the softened portion of said glass body to therebygradually form said glass body into a glass tube, the method comprising:when said boring jig is brought into contact with said glass body,applying voltages, in a longitudinal direction of said glass tube, tosaid glass body from electrodes provided on exteriors of a first endsurface and a second end surface in a longitudinal direction of saidglass body to thereby generate a voltage gradient.
 60. The method ofmanufacturing a glass tube according to claim 59, further comprising:after said glass tube is formed, removing at least an edge portion ofsaid glass tube at which the voltage gradient is set to be low.
 61. Anapparatus for manufacturing a glass tube, said apparatus having aheating element disposed around a columnar or a cylindrical glassmember, and also having a boring jig to be brought in contact with saidglass body heated by said heating element, said apparatus forming saidglass body gradually into a glass tube by contacting the boring jig tothe glass body, said apparatus further comprising: at least one pair ofelectrodes provided on an exterior of an outer circumferential surfaceof said glass body.
 62. The apparatus for manufacturing a glass tubeaccording to claim 61, wherein said boring jig is surface-treated and atleast a part of the boring jig, which makes contact with said glassbody, contains one of silicon carbide, pyrocarbon, and metallic carbide.63. An apparatus for manufacturing a glass tube, said apparatus having aheating element disposed around a columnar or a cylindrical glassmember, and also having a boring jig to be brought in contact with saidglass body heated by said heating element, said apparatus forming saidglass body gradually into a glass tube by contacting the boring jig tothe glass body, wherein said boring jig is an electrode, and anotherelectrode is provided on an outer circumferential side of said glassbody, or wherein electrodes are provided on an inner circumferentialside and the outer circumferential side of said glass tube.
 64. Theapparatus for manufacturing a glass tube according to claim 63, whereinsaid boring jig is surface-treated and at least a part of the boringjig, which makes contact with said glass body, contains one of siliconcarbide, pyrocarbon, and metallic carbide.
 65. An apparatus formanufacturing a glass tube, said apparatus having a heating elementdisposed around a columnar or a cylindrical glass member, and alsohaving a boring jig to be brought in contact with said glass body heatedby said heating element, said apparatus forming said glass bodygradually into a glass tube by contacting the boring jig to the glassbody, said apparatus further comprising: at least one pair of electrodesprovided on exteriors of both end surfaces in a longitudinal directionof said glass body.
 66. The apparatus for manufacturing a glass tubeaccording to claim 65, wherein said boring jig is surface-treated and atleast a part of the boring jig, which makes contact with said glassbody, contains one of silicon carbide, pyrocarbon, and metallic carbide.